Find direct PDF from page URL if Content-Type includes invalid parameter

The 'application/pdf' Content-Type shouldn't have any parameters, but a
site was returning 'application/pdf;charset=ISO-8859-1', so instead just
look for the 'application/pdf' prefix.

chrome/content/zotero/xpcom/attachments.js

@@ -1762,7 +1762,7 @@ Zotero.Attachments = new function(){
 					}
 					
 					// If DOI resolves directly to a PDF, save it to disk
-					if (contentType == 'application/pdf') {
+					if (contentType.startsWith('application/pdf')) {
 						Zotero.debug("URL resolves directly to PDF");
 						await Zotero.File.putContentsAsync(path, blob);
 						await _enforcePDF(path);