PHP 8.3 | Tokenizer/PHP + Generic/UnconditionalIfStatement: bug fix

When analyzing code during live coding, a situation could occur where the open parenthesis for an `if` control structure exists, but not a closing parenthesis.
In that case, `$end` would be set to `-1` (via `-- null`) and the `for` loop would never even run, but a warning would still be thrown for the code.

This warning is a false positive and should be avoided.

On top of that, PHP 8.3 deprecates the use of the increment/decrement operators on non-float/non-integer values, which can cause the below warning when running the sniff on PHP 8.3.
```
An error occurred during processing; checking has been aborted. The error message was:
Decrement on type null has no effect, this will change in the next major version of PHP in
path\to\src\Standards\Generic\Sniffs\CodeAnalysis\UnconditionalIfStatementSniff.php on line 72
```

Both the incorrect sniff warning, as well as the PHP 8.3 deprecation warning will now be avoided via the defensive coding added to the sniff.

When debugging the issue on the command line with the added test and using the following command `phpcs -ps ./generic/tests/codeanalysis/UnconditionalIfStatementUnitTest.inc --standard=Generic --sniffs=Generic.CodeAnalysis.UnconditionalIfStatement`, I was not receiving any output at all.

Digging deeper, I discovered two (loosely related) bugs in the Tokenizer/PHP class, which were the cause of that and which could be seen when running the tests:
```
Undefined array key 63

path\to\src\Tokenizers\PHP.php:3074
path\to\src\Tokenizers\Tokenizer.php:103
path\to\src\Files\File.php:577
path\to\src\Files\File.php:331
path\to\src\Files\LocalFile.php:92
path\to\tests\Standards\AbstractSniffUnitTest.php:175
path\to\tests\TestSuite7.php:28
```

This bug is fixed by fixing the incorrect comparison on line 3073.

... which then exposed the next bug:

```
Undefined array key 63

path\to\src\Tokenizers\PHP.php:3080
path\to\src\Tokenizers\Tokenizer.php:103
path\to\src\Files\File.php:577
path\to\src\Files\File.php:331
path\to\src\Files\LocalFile.php:92
path\to\tests\Standards\AbstractSniffUnitTest.php:175
path\to\tests\TestSuite7.php:28
```

... which is fixed by adding some extra defensive coding in the condition.

All three fixes are covered by the one test which was added.

src/Standards/Generic/Sniffs/CodeAnalysis/UnconditionalIfStatementSniff.php

@@ -64,7 +64,7 @@ public function process(File $phpcsFile, $stackPtr)
         $token  = $tokens[$stackPtr];
 
         // Skip if statement without body.
-        if (isset($token['parenthesis_opener']) === false) {
+        if (isset($token['parenthesis_opener'], $token['parenthesis_closer']) === false) {
             return;
         }
 

src/Standards/Generic/Tests/CodeAnalysis/UnconditionalIfStatementUnitTest.inc

@@ -10,4 +10,8 @@ if (true) {
 
 if (file_exists(__FILE__) === true) {
 
-}
+}
+
+// Intentional parse error/live coding.
+// This needs to be the last test in the file.
+if(true

src/Tokenizers/PHP.php

@@ -3130,14 +3130,16 @@ protected function processAdditional()
                 || $this->tokens[$i]['code'] === T_FALSE
                 || $this->tokens[$i]['code'] === T_NULL
             ) {
-                for ($x = ($i + 1); $i < $numTokens; $x++) {
+                for ($x = ($i + 1); $x < $numTokens; $x++) {
                     if (isset(Util\Tokens::$emptyTokens[$this->tokens[$x]['code']]) === false) {
                         // Non-whitespace content.
                         break;
                     }
                 }
 
-                if (isset($this->tstringContexts[$this->tokens[$x]['code']]) === true) {
+                if ($x !== $numTokens
+                    && isset($this->tstringContexts[$this->tokens[$x]['code']]) === true
+                ) {
                     if (PHP_CODESNIFFER_VERBOSITY > 1) {
                         $line = $this->tokens[$i]['line'];
                         $type = $this->tokens[$i]['type'];