validator: Don't fail validation if a snapshot release is missing a time

Resolves: #570, #650

Thanks to James Addison for the initial work!

src/as-validator-issue-tag.h

@@ -950,7 +950,13 @@ AsValidatorIssueTag as_validator_issue_tag_list[] =  {
 	{ "release-time-missing",
 	  AS_ISSUE_SEVERITY_ERROR,
 	  /* TRANSLATORS: Please do not translate AppStream tag and property names (in backticks). */
-	  N_("The release is missing either the `date` (preferred) or the `timestamp` property."),
+	  N_("The release entry is missing either the `date` (preferred) or the `timestamp` property."),
+	},
+
+	{ "release-time-missing-for-snapshot",
+	  AS_ISSUE_SEVERITY_INFO,
+	  /* TRANSLATORS: Please do not translate AppStream tag and property names (in backticks). */
+	  N_("The release entry is missing the `date` property. Ensure to add it before publishing the snapshot release."),
 	},
 
 	{ "release-timestamp-invalid",

src/as-validator.c

@@ -2453,7 +2453,10 @@ as_validator_check_release (AsValidator *validator, xmlNode *node, AsFormatStyle
 		g_autofree gchar *timestamp = as_xml_get_prop_value (node, "timestamp");
 		if (timestamp == NULL) {
 			/* Neither timestamp, nor date property exists */
-			as_validator_add_issue (validator, node, "release-time-missing", "date");
+			if (rel_kind == AS_RELEASE_KIND_SNAPSHOT)
+				as_validator_add_issue (validator, node, "release-time-missing-for-snapshot", "date");
+			else
+				as_validator_add_issue (validator, node, "release-time-missing", "date");
 		} else {
 			/* check if the timestamp is both a number and higher than 3000. The 3000 is used to check that it is not a year */
 			if (!as_str_verify_integer (timestamp, 3000, G_MAXINT64))