sigmffile: be more specific on except statement

This tries to catch the ValueError raised one line above. Be more
specifispecific about the exception type so as to not mask other error.

This is a preparatory change for the archive data file fix.

Signed-off-by: Liam Beguin <liambeguin@gmail.com>

Author: liambeguin

sigmf/sigmffile.py

@@ -531,8 +531,8 @@ def set_data_file(self, data_file=None, data_buffer=None, skip_checksum=False, o
                 buffer_count = -1 if mapped_length is None else mapped_length
                 raveled = np.frombuffer(self.data_buffer.getbuffer(), count=buffer_count, **common_args)
             else:
-                raise ValueError('In sigmffile.set_data_file(), either data_file or data_buffer must be not None')
-        except:  # TODO include likely exceptions here
+                raise SigMFFileError('In sigmffile.set_data_file(), either data_file or data_buffer must be not None')
+        except SigMFFileError:  # TODO include likely exceptions here
             warnings.warn('Failed to create data array from memory-map-file or buffer!')
         else:
             self._memmap = raveled.reshape(mapped_reshape)