soapy: fix segfault when launching and no device args where provided

lib/src/phy/rf/rf_soapy_imp.c

@@ -302,9 +302,10 @@ int rf_soapy_open_multi(char* args, void** h, uint32_t num_requested_channels)
   }
 
   // Select Soapy device by id
+  int dev_id = 0;
+  if (args != NULL) {
     const char dev_arg[] = "id=";
     char*      dev_ptr   = strstr(args, dev_arg);
-  int        dev_id    = 0;
     if (dev_ptr) {
       char dev_str[64] = {0};
       copy_subdev_string(dev_str, dev_ptr + strnlen(dev_arg, 64));
@@ -317,6 +318,7 @@ int rf_soapy_open_multi(char* args, void** h, uint32_t num_requested_channels)
       remove_substring(args, dev_arg);
       remove_substring(args, dev_str);
     }
+  }
 
   SoapySDRDevice* sdr = SoapySDRDevice_make(&(soapy_args[dev_id]));
   if (sdr == NULL) {