configure: Fix compile warning in PNG test

Fix compile warning (variable 'png_ptr' set but not used) in the
PNG detection test code.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Stefan Weil <sw@weilnetz.de>

1 files changed, 1 insertions, 1 deletions

diff --git a/configure b/configure
index 8a8ad27e20..b29cdd32df 100755
--- a/configure
+++ b/configure
@@ -1729,7 +1729,7 @@ cat > $TMPC <<EOF
 int main(void) {
     png_structp png_ptr;
     png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
-    return 0;
+    return png_ptr != 0;
 }
 EOF
   if $pkg_config libpng --modversion >/dev/null 2>&1; then