[BUGFIX] Fix broken back button in EXT:form

This patch fix a regression, introduced with #82668

Resolves: #83057
Related: #82668
Releases: master, 8.7
Change-Id: I421be116be6696c52733a77a94a61f81c84864f4
Reviewed-on: https://review.typo3.org/54716


Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Felix Nagel <info@felixnagel.com>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>

typo3/sysext/form/Resources/Private/Frontend/Partials/Form/Navigation.html

@@ -4,7 +4,8 @@
 		<div class="btn-group" role="group">
 			<f:if condition="{form.previousPage}">
 				<span class="previous">
-					<f:form.button property="__currentPage" value="{form.previousPage.index}" type="button" class="btn btn-cancel" formnovalidate="formnovalidate">{formvh:translateElementProperty(element: form.currentPage, renderingOptionProperty: 'previousButtonLabel')}</f:form.button>
+					<f:form.hidden property="__currentPage" value="{form.previousPage.index}" />
+					<f:form.button type="button" onclick="document.forms['{form.formDefinition.identifier}'].submit();" class="btn btn-cancel" formnovalidate="formnovalidate">{formvh:translateElementProperty(element: form.currentPage, renderingOptionProperty: 'previousButtonLabel')}</f:form.button>
 				</span>
 			</f:if>
 			<f:if condition="{form.nextPage}">