[vcs]: branchPopup reset exist selection onSpeedSearchPatternChanged

* branches are already sorted in priority order, so if no bestMatch
 we should use first one;
* (IDEA-166858) select first common branch appearance with speed search;

platform/dvcs-impl/src/com/intellij/dvcs/ui/BranchActionGroupPopup.java

@@ -227,6 +227,7 @@ public class BranchActionGroupPopup extends FlatSpeedSearchPopup {
 
   @Override
   protected void onSpeedSearchPatternChanged() {
+    getList().setSelectedIndex(0);
     super.onSpeedSearchPatternChanged();
     ScrollingUtil.ensureSelectionExists(getList());
   }