Prepend dot(.) if extension doesn't start with a dot.

Author: amvanbaren

server/src/main/java/org/eclipse/openvsx/ExtensionProcessor.java

@@ -448,6 +448,10 @@ private Map<String, String> parseContentTypesXml(byte[] content) {
                 var element = elements.item(i);
                 var attributes = element.getAttributes();
                 var extension = attributes.getNamedItem("Extension").getTextContent();
+                if(!extension.startsWith(".")) {
+                    extension = "." + extension;
+                }
+
                 var contentType = attributes.getNamedItem("ContentType").getTextContent();
                 contentTypes.put(extension, contentType);
             }