FileCheck: Fix off-by-one bug that made CHECK-NOT: ignore the next character after the colon.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164165 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/FileCheck/FileCheck.cpp b/utils/FileCheck/FileCheck.cpp
index 33f04ce..afbce35 100644
--- a/utils/FileCheck/FileCheck.cpp
+++ b/utils/FileCheck/FileCheck.cpp
@@ -537,11 +537,11 @@
       Buffer = Buffer.substr(CheckPrefix.size()+1);
     } else if (Buffer.size() > CheckPrefix.size()+6 &&
                memcmp(Buffer.data()+CheckPrefix.size(), "-NEXT:", 6) == 0) {
-      Buffer = Buffer.substr(CheckPrefix.size()+7);
+      Buffer = Buffer.substr(CheckPrefix.size()+6);
       IsCheckNext = true;
     } else if (Buffer.size() > CheckPrefix.size()+5 &&
                memcmp(Buffer.data()+CheckPrefix.size(), "-NOT:", 5) == 0) {
-      Buffer = Buffer.substr(CheckPrefix.size()+6);
+      Buffer = Buffer.substr(CheckPrefix.size()+5);
       IsCheckNot = true;
     } else {
       Buffer = Buffer.substr(1);