rev-parse: fix potential bus error with --parseopt option spec handling

A non-empty line containing no spaces should be treated by --parseopt as
an option group header, but was causing a bus error. Also added a test
script for rev-parse --parseopt.

Signed-off-by: Jay Soffian <jaysoffian@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-rev-parse.c

@@ -315,7 +315,7 @@ static int cmd_parseopt(int argc, const char **argv, const char *prefix)
 		s = strchr(sb.buf, ' ');
 		if (!s || *sb.buf == ' ') {
 			o->type = OPTION_GROUP;
-			o->help = xstrdup(skipspaces(s));
+			o->help = xstrdup(skipspaces(sb.buf));
 			continue;
 		}
 

t/t1502-rev-parse-parseopt.sh

@@ -0,0 +1,43 @@
+#!/bin/sh
+
+test_description='test git rev-parse --parseopt'
+. ./test-lib.sh
+
+cat > expect.err <<EOF
+usage: some-command [options] <args>...
+    
+    some-command does foo and bar!
+
+    -h, --help            show the help
+    --foo                 some nifty option --foo
+    --bar ...             some cool option --bar with an argument
+
+An option group Header
+    -C [...]              option C with an optional argument
+
+Extras
+    --extra1              line above used to cause a segfault but no longer does
+
+EOF
+
+test_expect_success 'test --parseopt help output' '
+	git rev-parse --parseopt -- -h 2> output.err <<EOF
+some-command [options] <args>...
+
+some-command does foo and bar!
+--
+h,help    show the help
+
+foo       some nifty option --foo
+bar=      some cool option --bar with an argument
+
+ An option group Header
+C?        option C with an optional argument
+
+Extras
+extra1    line above used to cause a segfault but no longer does
+EOF
+	git diff expect.err output.err
+'
+
+test_done