[file_qt4] Fix filename collision detection, broken on Windows

Qt uses forward slashes as directory separators on Windows as well, but
the path to the last read file (i.e. to the currently loaded file) may be
stored with backslashes. In this case we failed to detect name collision and
didn't automatically append _edit to the basename.

Canonicalize paths before comparing to make filename collision detection
more robust.

avidemux/qt4/ADM_userInterfaces/ADM_gui/file_qt4.cpp

@@ -39,9 +39,9 @@ static QWidget *fileSelGetParent(void)
  */
 static int fileSelWriteInternal(const char *label, char *target, uint32_t max, const char *location, const char *ext)
 {
-    QString str,outputPath,outputExt=QString("");
-    QString fileName,dot=QString(".");
-    QString separator = QString("/");
+    QString str,outputPath,outputExt; // null strings
+    QString fileName,dot = ".";
+    QString separator = "/"; // Qt uses forward slash on Windows too
     QString filterFile=QString::fromUtf8(QT_TRANSLATE_NOOP("qfile","All files (*.*)"));
     QFileDialog::Options opts = QFileDialog::Options();
     bool doFilter = !!(ext && strlen(ext));
@@ -106,18 +106,22 @@ static int fileSelWriteInternal(const char *label, char *target, uint32_t max, c
     if(outputPath.isEmpty() || !QDir(outputPath).exists())
         outputPath = QDir::homePath();
 
-    QString inputBaseName = QString("");
+    QString inputBaseName;
     std::string lastRead;
     admCoreUtils::getLastReadFile(lastRead);
     if(lastRead.size())
     {
         inputBaseName = QFileInfo(QString::fromUtf8(lastRead.c_str())).completeBaseName();
         str = outputPath+separator+inputBaseName+outputExt;
+        char *canonicalNew = ADM_PathCanonize(str.toUtf8().constData());
+        char *canonicalLast = ADM_PathCanonize(lastRead.c_str());
 
-        if(str==QString::fromUtf8(lastRead.c_str()))
+        if(!strcmp(canonicalNew, canonicalLast))
         { // try to avoid name collision when saving in the same directory as the currently loaded video
             str = outputPath+separator+inputBaseName+QString("_edit")+outputExt;
         }
+        delete [] canonicalNew;
+        delete [] canonicalLast;
     }else
     {
         str = QDir::homePath()+separator+QString("out")+dot+outputExt;