Fix off-by-one error in Regex::isValid

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187992 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/Regex.cpp b/lib/Support/Regex.cpp
index dec967e..5413641 100644
--- a/lib/Support/Regex.cpp
+++ b/lib/Support/Regex.cpp
@@ -43,7 +43,7 @@
   
   size_t len = llvm_regerror(error, preg, NULL, 0);
   
-  Error.resize(len);
+  Error.resize(len - 1);
   llvm_regerror(error, preg, &Error[0], len);
   return false;
 }