hw/sparc/leon3: Don't call get_image_size() on a NULL pointer

get_image_size() doesn't handle being passed a NULL pointer, so
avoid doing that. Spotted by the clang ub sanitizer (which notices
the attempt to pass NULL to open()).
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Message-id: 1470391439-28427-1-git-send-email-peter.maydell@linaro.org

hw/sparc/leon3.c

@@ -171,7 +171,11 @@ static void leon3_generic_hw_init(MachineState *machine)
     }
     filename = qemu_find_file(QEMU_FILE_TYPE_BIOS, bios_name);
 
-    bios_size = get_image_size(filename);
+    if (filename) {
+        bios_size = get_image_size(filename);
+    } else {
+        bios_size = -1;
+    }
 
     if (bios_size > prom_size) {
         fprintf(stderr, "qemu: could not load prom '%s': file too big\n",