A '<' with a trigraph '#' is not a valid editor placeholder

Credit to OSS-Fuzz for discovery:
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=3137#c5

rdar://34923985

llvm-svn: 315398
diff --git a/clang/lib/Lex/Lexer.cpp b/clang/lib/Lex/Lexer.cpp
index 9885ab9..0c179c0 100644
--- a/clang/lib/Lex/Lexer.cpp
+++ b/clang/lib/Lex/Lexer.cpp
@@ -3542,7 +3542,8 @@
     } else if (LangOpts.Digraphs && Char == '%') {     // '<%' -> '{'
       CurPtr = ConsumeChar(CurPtr, SizeTmp, Result);
       Kind = tok::l_brace;
-    } else if (Char == '#' && lexEditorPlaceholder(Result, CurPtr)) {
+    } else if (Char == '#' && /*Not a trigraph*/ SizeTmp == 1 &&
+               lexEditorPlaceholder(Result, CurPtr)) {
       return true;
     } else {
       Kind = tok::less;