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

@@ -775,6 +775,7 @@ async def send_block(self, data):
     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