dshow: fix return code when opening device

Successfully opening a device altered the ret variable, making the function
not cleanup properly and return an incorrect value for errors that happened
afterwards.
Reviewed-by: Stefano Sabatini <stefasab@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavdevice/dshow.c

@@ -929,20 +929,18 @@ static int dshow_read_header(AVFormatContext *avctx)
     }
 
     if (ctx->device_name[VideoDevice]) {
-        ret = dshow_open_device(avctx, devenum, VideoDevice);
-        if (ret < 0)
-            goto error;
-        ret = dshow_add_device(avctx, VideoDevice);
-        if (ret < 0)
+        if ((r = dshow_open_device(avctx, devenum, VideoDevice)) < 0 ||
+            (r = dshow_add_device(avctx, VideoDevice)) < 0) {
+            ret = r;
             goto error;
+        }
     }
     if (ctx->device_name[AudioDevice]) {
-        ret = dshow_open_device(avctx, devenum, AudioDevice);
-        if (ret < 0)
-            goto error;
-        ret = dshow_add_device(avctx, AudioDevice);
-        if (ret < 0)
+        if ((r = dshow_open_device(avctx, devenum, AudioDevice)) < 0 ||
+            (r = dshow_add_device(avctx, AudioDevice)) < 0) {
+            ret = r;
             goto error;
+        }
     }
 
     ctx->mutex = CreateMutex(NULL, 0, NULL);