Git: fix archive file name

When a filename such as a.tar.gz is given and the filter tar.gz is
selected, Qt Creator generated a.tar.gz.tar.gz because string from the
filter doesn't start with a "." and QFileInfo::completeSuffix() starts with
a ".".

Change-Id: I58fedf79a88b25cd595e17adb8d5660e066658f0
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/git/gitclient.cpp

@@ -1248,7 +1248,7 @@ void GitClient::archive(const QString &workingDirectory, QString commit)
         return;
     QString extension = filters.value(selectedFilter);
     QFileInfo archive(archiveName);
-    if (archive.completeSuffix() != extension) {
+    if (extension != "." + archive.completeSuffix()) {
         archive = QFileInfo(archive.filePath() + extension);
     }