Make sure we don't resize(0) when we get a fwdref with Idx == UINT_MAX

Make it an error instead.

Bug found with AFL fuzz.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@236190 91177308-0d34-0410-b5e6-96231b3b80d8

test/Bitcode/invalid.test

@@ -112,3 +112,8 @@ RUN: not llvm-dis -disable-output %p/Inputs/invalid-array-op-not-2nd-to-last.bc
 RUN:   FileCheck --check-prefix=ARRAY-NOT-2LAST %s
 
 ARRAY-NOT-2LAST: Array op not second to last
+
+RUN: not llvm-dis -disable-output %p/Inputs/invalid-too-big-fwdref.bc 2>&1 | \
+RUN:   FileCheck --check-prefix=HUGE-FWDREF %s
+
+HUGE-FWDREF: Invalid record