apply --whitespace: warn blank but not necessarily empty lines at EOF

The whitespace error of adding blank lines at the end of file should
trigger if you added a non-empty line at the end, if the contents of the
line is full of whitespaces.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin-apply.c

@@ -1957,7 +1957,8 @@ static int apply_one_fragment(struct image *img, struct fragment *frag,
 			is_blank_context = 1;
 			break;
 		case ' ':
-			if (plen && patch[1] == '\n')
+			if (plen && (ws_rule & WS_BLANK_AT_EOF) &&
+			    ws_blank_line(patch + 1, plen, ws_rule))
 				is_blank_context = 1;
 		case '-':
 			memcpy(old, patch + 1, plen);
@@ -1985,7 +1986,8 @@ static int apply_one_fragment(struct image *img, struct fragment *frag,
 				      (first == '+' ? 0 : LINE_COMMON));
 			new += added;
 			if (first == '+' &&
-			    added == 1 && new[-1] == '\n')
+			    (ws_rule & WS_BLANK_AT_EOF) &&
+			    ws_blank_line(patch + 1, plen, ws_rule))
 				added_blank_line = 1;
 			break;
 		case '@': case '\\':

t/t4124-apply-ws-rule.sh

@@ -227,4 +227,17 @@ test_expect_success 'blank at EOF with --whitespace=error' '
 	grep "new blank line at EOF" error
 '
 
+test_expect_success 'blank but not empty at EOF' '
+	{ echo a; echo b; echo c; } >one &&
+	git add one &&
+	echo "   " >>one &&
+	cat one >expect &&
+	git diff -- one >patch &&
+
+	git checkout one &&
+	git apply --whitespace=warn patch 2>error &&
+	test_cmp expect one &&
+	grep "new blank line at EOF" error
+'
+
 test_done