Don't save context chunks

Otherwise the saved patch file contains the whole contents
of the compared files.

Change-Id: I0f2d4c4e9b2c56ceab2b1e312e0895087060d0dc
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/diffeditor/diffutils.cpp

@@ -353,6 +353,9 @@ QString DiffUtils::makePatchLine(const QChar &startLineCharacter,
 QString DiffUtils::makePatch(const ChunkData &chunkData,
                              bool lastChunk)
 {
+    if (chunkData.contextChunk)
+        return QString();
+
     QString diffText;
     int leftLineCount = 0;
     int rightLineCount = 0;