[5.4] Makes cache() throw exceoption when incorrect first argument

The cache() function will return nothing when the first argument is something else than a string or array.

This PR fixes that by throwing an exception when that is the case.
It also improves code styling by removing the nested ifs (so less indentation) and follows the 'golden path' guideline.

src/Illuminate/Foundation/helpers.php

@@ -231,15 +231,19 @@ function cache()
             return app('cache')->get($arguments[0], isset($arguments[1]) ? $arguments[1] : null);
         }
 
-        if (is_array($arguments[0])) {
-            if (! isset($arguments[1])) {
-                throw new Exception(
-                    'You must set an expiration time when putting to the cache.'
-                );
-            }
+        if (! is_array($arguments[0])) {
+            throw new Exception(
+                'The argument passed to the cache must be a string or an array.'
+            );
+        }
 
-            return app('cache')->put(key($arguments[0]), reset($arguments[0]), $arguments[1]);
+        if (! isset($arguments[1])) {
+            throw new Exception(
+                'You must set an expiration time when putting to the cache.'
+            );
         }
+
+        return app('cache')->put(key($arguments[0]), reset($arguments[0]), $arguments[1]);
     }
 }