Prefer implicit false over None check

This patch prefers an implicit False comparison in regalloc_trace_worker
rather than just checking if the value is None. This protects against
other values that end up being false and makes us more consistent with
the Google Python style guide.

Author: boomanaiden154

compiler_opt/es/regalloc_trace/regalloc_trace_worker.py

@@ -153,7 +153,7 @@ def __init__(
     self._clang_path = clang_path
     self._basic_block_trace_model_path = basic_block_trace_model_path
     self._thread_count = thread_count
-    self._extra_bb_trace_model_flags = ([] if extra_bb_trace_model_flags is None
+    self._extra_bb_trace_model_flags = ([] if not extra_bb_trace_model_flags
                                         else extra_bb_trace_model_flags)
 
     self._has_local_corpus = False