[Bitcode] Don't assert on invalid attribute group record

Report an error instead.

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

@@ -1647,9 +1647,7 @@ Error BitcodeReader::parseAttributeGroupBlock() {
           }
 
           B.addAttribute(KindStr.str(), ValStr.str());
-        } else {
-          assert((Record[i] == 5 || Record[i] == 6) &&
-                 "Invalid attribute group entry");
+        } else if (Record[i] == 5 || Record[i] == 6) {
           bool HasType = Record[i] == 6;
           Attribute::AttrKind Kind;
           if (Error Err = parseAttrKind(Record[++i], &Kind))
@@ -1658,6 +1656,8 @@ Error BitcodeReader::parseAttributeGroupBlock() {
             return error("Not a type attribute");
 
           B.addTypeAttr(Kind, HasType ? getTypeByID(Record[++i]) : nullptr);
+        } else {
+          return error("Invalid attribute group entry");
         }
       }