radio,uhd: catch exception returned when parsing bad device args string

fix segfault when device args are malformed

Warning: Scheduling priority of UHD not changed. Cause: Not enough privileges.
terminate called after throwing an instance of 'uhd::value_error'
  what():  ValueError: invalid args string: type=b200,num_recv_frames=64,num_send_frames=64 --otw_format=sc12
Stack trace (most recent call last):
    | Source "./nptl/pthread_kill.c", line 78, in __pthread_kill_implementation
      Source "./nptl/pthread_kill.c", line 44, in __pthread_kill [0x7faa57cb1a7c]

Author: andrepuschmann

lib/radio/uhd/radio_uhd_device.h

@@ -54,7 +54,10 @@ class radio_uhd_device : public uhd_exception_handler
   bool usrp_make(const std::string& device_address)
   {
     // Parse args into dictionary.
-    uhd::device_addr_t device_addr(device_address);
+    uhd::device_addr_t device_addr;
+    if (!safe_execution([device_address, &device_addr]() { device_addr = uhd::device_addr_t(device_address); })) {
+      return false;
+    }
 
     // Destroy any previous USRP instance
     usrp = nullptr;