Correction is passed file name to checkPageExistsUsingTitle, function expects file name prefixed with File: (#3194)

Author: ashishkumar468

app/src/main/java/fr/free/nrw/commons/upload/UploadService.java

@@ -309,7 +309,7 @@ private String findUniqueFilename(String fileName) throws IOException {
                     sequenceFileName = regexMatcher.replaceAll("$1 " + sequenceNumber + "$2");
                 }
             }
-            if (!mediaClient.checkPageExistsUsingTitle(sequenceFileName).blockingGet()
+            if (!mediaClient.checkPageExistsUsingTitle(String.format("File:%s",sequenceFileName)).blockingGet()
                     && !unfinishedUploads.contains(sequenceFileName)) {
                 break;
             }