Git: Fix detection of line with whitespace in commit highlighter

Git strips trailing whitespace.

Change-Id: Ie0d3fa85007d4cd3646424faa772a904edc55966
Reviewed-by: Tobias Hunger <tobias.hunger@theqtcompany.com>

src/plugins/git/githighlighters.cpp

@@ -56,7 +56,7 @@ void GitSubmitHighlighter::highlightBlock(const QString &text)
 {
     // figure out current state
     State state = static_cast<State>(previousBlockState());
-    if (text.isEmpty()) {
+    if (text.trimmed().isEmpty()) {
         if (state == Header)
             state = Other;
         setCurrentBlockState(state);