run-mypy: Deindent a bit of logic by moving an exit path up.

tools/run-mypy

@@ -83,6 +83,9 @@ files_dict = cast(Dict[str, List[str]],
 pyi_files = set(files_dict['pyi'])
 python_files = [fpath for fpath in files_dict['py']
                 if not fpath.endswith('.py') or fpath + 'i' not in pyi_files]
+if not python_files:
+    print("There are no files to run mypy on.")
+    sys.exit(0)
 
 extra_args = ["--check-untyped-defs",
               "--follow-imports=silent",
@@ -102,17 +105,14 @@ if args.ignore_missing_imports:
 if args.quick:
     extra_args.append("--quick")
 
+rc = subprocess.call([mypy_command] + extra_args + python_files)
 
-# run mypy
-if python_files:
-    rc = subprocess.call([mypy_command] + extra_args + python_files)
-    if args.linecoverage_report:
-        # Move the coverage report to where codecov will look for it.
-        try:
-            os.rename('var/linecoverage-report/coverage.txt', 'var/.coverage')
-        except OSError:
-            # maybe mypy crashed; exit with its error code
-            pass
-    sys.exit(rc)
-else:
-    print("There are no files to run mypy on.")
+if args.linecoverage_report:
+    # Move the coverage report to where codecov will look for it.
+    try:
+        os.rename('var/linecoverage-report/coverage.txt', 'var/.coverage')
+    except OSError:
+        # maybe mypy crashed; exit with its error code
+        pass
+
+sys.exit(rc)