vcap/avfoundation: fixed cmdline dev spec parsing

fixed commits from 2023-01-03 (a9c001b and 4a91545):

1. unspecified device index is -1, not 0; this fixes run without device
spec (`-t avfoundation`)

2. device_name was not include in the condition for explicit device
selection. It coincidentally worked because of the bug nr. 1, because
the device_index was set to -1 and checked to not equal 0, which fulfills
the if condition

Author: MartinPulec

src/video_capture/avfoundation.mm

@@ -247,7 +247,8 @@ - (id)initWithParams: (NSDictionary *) params
         int device_idx = [params valueForKey:@"device"] ? [[params valueForKey:@"device"] intValue] : -1;
         NSString *device_uid = [params valueForKey:@"uid"];
         NSString *device_name = [params valueForKey:@"name"];
-        if (device_idx != 0 || device_uid) {
+        if (device_idx != -1 || device_name != nullptr ||
+            device_uid != nullptr) {
                 int i = -1;
                 for (AVCaptureDevice *device in [vidcap_avfoundation_state devices]) {
                         i++;