regcomp can read past end of string after parsing flags

New test in 8a6d8ec6fe revealed additional code problem reading past
end of string under clang with sanitize=address.

1 files changed, 2 insertions, 1 deletions

diff --git a/regcomp.c b/regcomp.c
index e069a15d32..9e1fab9e89 100644
--- a/regcomp.c
+++ b/regcomp.c
@@ -10414,7 +10414,8 @@ S_reg(pTHX_ RExC_state_t *pRExC_state, I32 paren, I32 *flagp,U32 depth)
               parse_flags:
 		parse_lparen_question_flags(pRExC_state);
                 if (UCHARAT(RExC_parse) != ':') {
-                    nextchar(pRExC_state);
+                    if (*RExC_parse)
+                        nextchar(pRExC_state);
                     *flagp = TRYAGAIN;
                     return NULL;
                 }