connections: reset log file on run

This avoids problems if a large log file upload was cancelled on a previous run, leaving the file still open.

Author: laurensvalk

pybricksdev/connections.py

@@ -271,6 +271,7 @@ async def run(self, py_path, wait=True, print_output=True):
         """
 
         # Reset output buffer
+        self.log_file = None
         self.output = []
         self.print_output = print_output