GUI: Remeber last path where project file was opened from.

It is handy to remember the last location of the opened project file.
Currently the Open Project -dialog was always opened to location of
the executable file. Which is never the correct place. But last
opened project file location might at least be near the location user
wants to open next.

Ticket: danmar#3493 (GUI: remember last path in Open Project File)

gui/common.h

@@ -81,6 +81,7 @@
 #define PROGRESS_MAX                    1024.0
 
 #define SETTINGS_CHECKED_PLATFORM       "Checked platform"
+#define SETTINGS_LAST_PROJECT_PATH      "Last project path"
 
 /// @}
 #endif

gui/mainwindow.cpp

@@ -848,14 +848,19 @@ void MainWindow::OpenOnlineHelp()
 
 void MainWindow::OpenProjectFile()
 {
+    const QString lastPath = mSettings->value(SETTINGS_LAST_PROJECT_PATH, QString()).toString();
     const QString filter = tr("Project files (*.cppcheck);;All files(*.*)");
-    QString filepath = QFileDialog::getOpenFileName(this,
-                       tr("Select Project File"),
-                       QString(),
-                       filter);
+    const QString filepath = QFileDialog::getOpenFileName(this,
+                             tr("Select Project File"),
+                             lastPath,
+                             filter);
 
     if (!filepath.isEmpty()) {
-        LoadProjectFile(filepath);
+        const QFileInfo fi(filepath);
+        if (fi.exists() && fi.isFile() && fi.isReadable()) {
+            mSettings->setValue(SETTINGS_LAST_PROJECT_PATH, fi.path());
+            LoadProjectFile(filepath);
+        }
     }
 }