scripts: compliance: Avoid exception when commit message body is empty

Avoid the following exception in the Identity test when the commit body
is empty:

Traceback (most recent call last):
  File "/Users/carles/src/zephyr/zephyr/../zephyr/scripts/ci/check_compliance.py", line 2053, in main
    n_fails = _main(args)
              ^^^^^^^^^^^
  File "/Users/carles/src/zephyr/zephyr/../zephyr/scripts/ci/check_compliance.py", line 1988, in _main
    test.run()
  File "/Users/carles/src/zephyr/zephyr/../zephyr/scripts/ci/check_compliance.py", line 1459, in run
    auth_name, auth_email, body = git(
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^
ValueError: not enough values to unpack (expected 3, got 2)

Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>

Author: carlescufi

scripts/ci/check_compliance.py

@@ -1456,9 +1456,12 @@ class Identity(ComplianceTest):
 
     def run(self):
         for shaidx in get_shas(COMMIT_RANGE):
+            commit_info = git('show', '-s', '--format=%an%n%ae%n%b', shaidx).split('\n', 2)
+
+            if len(commit_info) != 3:
+                failures.append(f'{shaidx}: Empty commit message body')
+
             auth_name, auth_email, body = git(
-                'show', '-s', '--format=%an%n%ae%n%b', shaidx
-            ).split('\n', 2)
 
             match_signoff = re.search(r"signed-off-by:\s(.*)", body,
                                       re.IGNORECASE)