clang-format: Fix excessive formatting caused by r195954.

Due to a bug in the patch, clang-format would more or less simply format
all multi-line comments.

llvm-svn: 196080
diff --git a/clang/lib/Format/Format.cpp b/clang/lib/Format/Format.cpp
index 7f91239..28ef19e 100644
--- a/clang/lib/Format/Format.cpp
+++ b/clang/lib/Format/Format.cpp
@@ -1457,6 +1457,7 @@
     bool IsContinuedComment = Line->First->is(tok::comment) &&
                               Line->First->Next == NULL &&
                               Line->First->NewlinesBefore < 2 && PreviousLine &&
+                              PreviousLine->Affected &&
                               PreviousLine->Last->is(tok::comment);
 
     if (SomeTokenAffected || SomeFirstChildAffected || LineMoved ||