[PATCH v3 1/4] difftool: silence uninitialized variable warning

Git::config() returns `undef` when given keys that do not exist.
Check that the $guitool value is defined to prevent a noisy
"Use of uninitialized variable $guitool in length" warning.

Signed-off-by: David Aguilar <redacted>
---
Unchanged since v1.

 git-difftool.perl | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/git-difftool.perl b/git-difftool.perl
index 0a90de4..12231fb 100755
--- a/git-difftool.perl
+++ b/git-difftool.perl

@@ -336,7 +336,7 @@ sub main
 	}
 	if ($opts{gui}) {
 		my $guitool = Git::config('diff.guitool');
-		if (length($guitool) > 0) {
+		if (defined($guitool) && length($guitool) > 0) {
 			$ENV{GIT_DIFF_TOOL} = $guitool;
 		}
 	}

-- 
1.8.2.rc0.20.gf548dd7