[TASK] Add possibility to add a fallback html template

Classes/Service/MailTemplateService.php

@@ -301,7 +301,13 @@ class MailTemplateService {
 					$defaultTemplateContent = self::getRegisterArray(
 					)[$this->extensionKey][$this->templateName]['templateContent'];
 				} else {
-					return FALSE;
+
+					$defaultTemplateFile = $GLOBALS['TYPO3_CONF_VARS']['MAIL']['defaultHtmlTemplate'];
+					if (file_exists($defaultTemplateFile)) {
+						$defaultTemplateContent = file_get_contents($defaultTemplateFile);
+					} else {
+						return FALSE;
+					}
 				}
 			}
 		} elseif (filter_var($template->getToAddress(), FILTER_VALIDATE_EMAIL)) {

Configuration/TypoScript/setup.ts

@@ -18,6 +18,9 @@ module.tx_sgmail {
 
 			# extension where automatic generated registrations from forms are put. gets appended with /Configuration/MailTemplates/. make sure these folders exist!
 			configurationLocation = project_theme
+
+			# default html template file, which serves as a fallback for all mail templates
+			defaultHtmlTemplate = EXT:project_theme/Configuration/MailTemplates/Default.html
 		}
 
 		# default template language