patch 9.1.0701: crash with NFA regex engine when searching for composing chars

Problem:  crash with NFA regex engine when searching for composing chars
          (SuyueGuo)
Solution: When there is no composing character, break out of the loop
          and check that out1 state is not null

fixes: #15583

Signed-off-by: Christian Brabandt <cb@256bit.org>

src/regexp_nfa.c

@@ -6525,7 +6525,8 @@ nfa_regmatch(
 			else
 			    result = FAIL;
 
-			if (t->state->out->out1->c == NFA_END_COMPOSING)
+			if (t->state->out->out1 != NULL
+				&& t->state->out->out1->c == NFA_END_COMPOSING)
 			{
 			    end = t->state->out->out1;
 			    ADD_STATE_IF_MATCH(end);

src/testdir/test_crash.vim

@@ -228,6 +228,11 @@ func Test_crash1_3()
   call term_sendkeys(buf, args)
   call TermWait(buf, 50)
 
+  let file = 'crash/nullptr_regexp_nfa'
+  let cmn_args = "%s -u NONE -i NONE -n -X -m -n -e -s -S %s -c ':qa!'"
+  let args = printf(cmn_args, vim, file)
+  call term_sendkeys(buf, args)
+  call TermWait(buf, 50)
 
   " clean up
   exe buf .. "bw!"

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    701,
 /**/
     700,
 /**/