Fix another clang-format crasher related to multi-line comments.

This fixes:
/*
*
* something long going over the column limit.
*/

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@182932 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Format/BreakableToken.cpp b/lib/Format/BreakableToken.cpp
index 01317db..8672ece 100644
--- a/lib/Format/BreakableToken.cpp
+++ b/lib/Format/BreakableToken.cpp
@@ -241,6 +241,9 @@
       Lines[i] = Lines[i].substr(Offset);
       LeadingWhitespace[i] += Offset;
     }
+    // Exclude empty lines from the calculation of the left-most column.
+    if (Lines[i].empty())
+      continue;
     IndentAtLineBreak = std::min<int>(IndentAtLineBreak, StartOfLineColumn[i]);
   }
   DEBUG({