further bug fixes when using context path (#1475)

Co-authored-by: Anthony Stirling <77850077+Frooodle@users.noreply.github.com>

src/main/resources/templates/convert/pdf-to-img.html

@@ -18,7 +18,7 @@
                 <span class="tool-header-text" th:text="#{pdfToImage.header}"></span>
               </div>
               <p th:text="#{processTimeWarning}"></p>
-              <form method="post" enctype="multipart/form-data" th:action="@{api/v1/convert/pdf/img}">
+              <form method="post" enctype="multipart/form-data" th:action="@{'/api/v1/convert/pdf/img'}">
                 <div th:replace="~{fragments/common :: fileSelector(name='fileInput', multiple=false, accept='application/pdf')}"></div>
                 <div class="mb-3">
                   <label th:text="#{pdfToImage.selectText}"></label>