patch 8.2.2177: pattern "^" does not match if first character is combining

Problem:    Pattern "^" does not match if the first character in the line is
            combining. (Rene Kita)
Solution:   Do accept a match at the start of the line. (closes #6963)
diff --git a/src/regexp_nfa.c b/src/regexp_nfa.c
index cbfed49..6182f58 100644
--- a/src/regexp_nfa.c
+++ b/src/regexp_nfa.c
@@ -5754,9 +5754,11 @@
 	    {
 	    case NFA_MATCH:
 	      {
-		// If the match ends before a composing characters and
-		// rex.reg_icombine is not set, that is not really a match.
-		if (enc_utf8 && !rex.reg_icombine && utf_iscomposing(curc))
+		// If the match is not at the start of the line, ends before a
+		// composing characters and rex.reg_icombine is not set, that
+		// is not really a match.
+		if (enc_utf8 && !rex.reg_icombine
+			     && rex.input != rex.line && utf_iscomposing(curc))
 		    break;
 
 		nfa_match = TRUE;