Previously if no device tree was passed to microblaze_load_kernel() then
qemu_find_file() would try to find a NULL pointer. To avoid this put a
check around qemu_find_file().

Signed-off-by: Alistair Francis <alistair.francis@xilinx.com>
Reported-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---

 hw/microblaze/boot.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/microblaze/boot.c b/hw/microblaze/boot.c
index 457a08a2fe..35bfeda7aa 100644
--- a/hw/microblaze/boot.c
+++ b/hw/microblaze/boot.c
@@ -124,7 +124,7 @@ void microblaze_load_kernel(MicroBlazeCPU *cpu, hwaddr ddr_base,
     kernel_cmdline = qemu_opt_get(machine_opts, "append");
     dtb_arg = qemu_opt_get(machine_opts, "dtb");
     /* default to pcbios dtb as passed by machine_init */
-    if (!dtb_arg) {
+    if (!dtb_arg && dtb_filename) {
         filename = qemu_find_file(QEMU_FILE_TYPE_BIOS, dtb_filename);
     }
 
-- 
2.14.1