Fix bug in getDiffChunk()

The binary search was returning null when a line is part of a
diff chunk, causing regression in resizePaddingWidget() for
comment boxes. Fixed by adding an extra check.

Change-Id: I3b0e30173f8cea773d3804abc3ecfea4ef67123d

gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/SideBySide2.java

@@ -1176,7 +1176,18 @@ public class SideBySide2 extends Screen {
         diffChunks,
         new DiffChunkInfo(side, line, 0, false), // Dummy DiffChunkInfo
         getDiffChunkComparator());
-    return res >= 0 ? diffChunks.get(res) : null;
+    if (res >= 0) {
+      return diffChunks.get(res);
+    } else { // The line might be within a DiffChunk
+      res = -res - 1;
+      if (res > 0) {
+        DiffChunkInfo info = diffChunks.get(res - 1);
+        if (info.side == side && info.start <= line && line <= info.end) {
+          return info;
+        }
+      }
+    }
+    return null;
   }
 
   private int getWrapAroundDiffChunkIndex(int index) {