Allow translator based header fix up to go wrong

It's possible that some headers are so broken that the
code trying to fix them up can't work out something.
A date is a good example since an error parsing a date
in a header will cause many date-based corrections to
fail.

Log the problem and hope that a file-based correction
is put in place that allows the translator code to
function properly.

python/astro_metadata_translator/headers.py

@@ -353,6 +353,12 @@ class or else support automatic translation class determination.
         modified = _find_from_resource(header, *translator.resource_root(), target_file)
 
     # Allow a translation class to do local fixups
-    translator_modified = translator_class.fix_header(header)
+    # Allow it to fail but log the failure
+    try:
+        translator_modified = translator_class.fix_header(header)
+    except Exception as e:
+        log.fatal("Ignoring translator header fixup of %s %s: %s",
+                  instrument, obsid, str(e))
+        translator_modified = False
 
     return modified | translator_modified

tests/test_headers.py

@@ -29,6 +29,16 @@ def fix_header(cls, header):
         return True
 
 
+class AlsoNotDecamTranslator(DecamTranslator):
+    """This is a DECam translator with override list of header corrections
+    that fails."""
+    name = None
+
+    @classmethod
+    def fix_header(cls, header):
+        raise RuntimeError("Failure to work something out from header")
+
+
 class HeadersTestCase(unittest.TestCase):
 
     def setUp(self):
@@ -360,6 +370,12 @@ def test_translator_fix_header(self):
         self.assertTrue(fixed)
         self.assertEqual(header["DTSITE"], "hi")
 
+        header["DTSITE"] = "reset"
+        with self.assertLogs("astro_metadata_translator", level="FATAL"):
+            fixed = fix_header(header, translator_class=AlsoNotDecamTranslator)
+        self.assertFalse(fixed)
+        self.assertEqual(header["DTSITE"], "reset")
+
 
 if __name__ == "__main__":
     unittest.main()