patch 8.2.2181: valgrind warnings for using uninitialized value

Problem:    Valgrind warnings for using uninitialized value.
Solution:   Do not use "start" or "end" unless there is a match.
diff --git a/src/regexp_nfa.c b/src/regexp_nfa.c
index 6182f58..ad47142 100644
--- a/src/regexp_nfa.c
+++ b/src/regexp_nfa.c
@@ -7227,21 +7227,24 @@
 #endif
 
 theend:
-    // Make sure the end is never before the start.  Can happen when \zs and
-    // \ze are used.
-    if (REG_MULTI)
+    if (retval > 0)
     {
-	lpos_T *start = &rex.reg_mmatch->startpos[0];
-	lpos_T *end = &rex.reg_mmatch->endpos[0];
+	// Make sure the end is never before the start.  Can happen when \zs and
+	// \ze are used.
+	if (REG_MULTI)
+	{
+	    lpos_T *start = &rex.reg_mmatch->startpos[0];
+	    lpos_T *end = &rex.reg_mmatch->endpos[0];
 
-	if (end->lnum < start->lnum
+	    if (end->lnum < start->lnum
 			|| (end->lnum == start->lnum && end->col < start->col))
-	    rex.reg_mmatch->endpos[0] = rex.reg_mmatch->startpos[0];
-    }
-    else if (retval > 0)
-    {
-	if (rex.reg_match->endp[0] < rex.reg_match->startp[0])
-	    rex.reg_match->endp[0] = rex.reg_match->startp[0];
+		rex.reg_mmatch->endpos[0] = rex.reg_mmatch->startpos[0];
+	}
+	else
+	{
+	    if (rex.reg_match->endp[0] < rex.reg_match->startp[0])
+		rex.reg_match->endp[0] = rex.reg_match->startp[0];
+	}
     }
 
     return retval;