Bugfix: GET on incomplete file would keep it locked indefinitely

If a GET arrived before a file was complete, we would miss to unlock
it due to the fcore pointer missing in the response struct.

src/tus_request.c

@@ -379,12 +379,13 @@ tus_request(VRT_CTX, struct VPFX(tus_server) *tussrv,
 			r->status = 404;
 			return (0);
 		}
+		AN(fcore);
 		AN(fdisk);
 		if (fdisk->location_length > 0) {
-			/* done file */
 			r->fcore = fcore;
-			r->status = 301;
+			r->status = 301;	/* done file */
 		} else {
+			AZ(pthread_mutex_unlock(&fcore->mtx));
 			r->status = 400;
 		}
 		return (0);

src/vtc/plain.vtc

@@ -170,6 +170,11 @@ client c2 {
 	expect resp.http.has-filenamee == false
 	expect resp.http.has-filenam == false
 
+	# failing get on upload in progress
+	txreq -url "/vtc"
+	rxresp
+	expect resp.status == 400
+
 	# finish upload
 	txreq	-method PATCH -url "/vtc" \
 		-hdr "Tus-Resumable: 1.0.0" \