Merge branch 'jk/add-p-commentchar-fix' into maint

"git add -p" were updated in 2.12 timeframe to cope with custom
core.commentchar but the implementation was buggy and a
metacharacter like $ and * did not work.

* jk/add-p-commentchar-fix:
  add--interactive: quote commentChar regex
  add--interactive: handle EOF in prompt_yesno

git-add--interactive.perl

@@ -1085,7 +1085,7 @@ EOF2
 
 	open $fh, '<', $hunkfile
 		or die sprintf(__("failed to open hunk edit file for reading: %s"), $!);
-	my @newtext = grep { !/^$comment_line_char/ } <$fh>;
+	my @newtext = grep { !/^\Q$comment_line_char\E/ } <$fh>;
 	close $fh;
 	unlink $hunkfile;
 
@@ -1140,6 +1140,7 @@ sub prompt_yesno {
 	while (1) {
 		print colored $prompt_color, $prompt;
 		my $line = prompt_single_character;
+		return undef unless defined $line;
 		return 0 if $line =~ /^n/i;
 		return 1 if $line =~ /^y/i;
 	}

t/t3701-add-interactive.sh

@@ -477,4 +477,12 @@ test_expect_success 'add -p does not expand argument lists' '
 	! grep not-changed trace.out
 '
 
+test_expect_success 'hunk-editing handles custom comment char' '
+	git reset --hard &&
+	echo change >>file &&
+	test_config core.commentChar "\$" &&
+	echo e | GIT_EDITOR=true git add -p &&
+	git diff --exit-code
+'
+
 test_done