Don't crash in case of unexpected build date format

try to parse the date, if unsuccessful, give up instead of crashing
entirely

openqabot/approver.py

@@ -165,7 +165,11 @@ def was_ok_before(self, failed_job_id: int, inc: int) -> bool:
             return False
 
         current_build = older_jobs["data"][0]["build"][:-2]
-        current_build_date = datetime.strptime(current_build, "%Y%m%d")
+        try:
+            current_build_date = datetime.strptime(current_build, "%Y%m%d")
+        except (ValueError, TypeError):
+            log.info("Could not parse build date %s", current_build)
+            return False
 
         # Use at most X days old build. Don't go back in time too much to reduce risk of using invalid tests
         oldest_build_usable = current_build_date - timedelta(
@@ -177,7 +181,11 @@ def was_ok_before(self, failed_job_id: int, inc: int) -> bool:
         for i in range(1, len(older_jobs["data"])):
             job = older_jobs["data"][i]
             job_build = job["build"][:-2]
-            job_build_date = datetime.strptime(job_build, "%Y%m%d")
+            try:
+                job_build_date = datetime.strptime(job_build, "%Y%m%d")
+            except (ValueError, TypeError):
+                log.info("Could not parse build date %s", current_build)
+                continue
 
             # Check the job is not too old
             if job_build_date < oldest_build_usable: