qt-faststart: check return of ftello()

Fixes CID739863
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

tools/qt-faststart.c

@@ -137,11 +137,11 @@ int main(int argc, char *argv[])
                 goto error_out;
             }
             if (   fseeko(infile, -ATOM_PREAMBLE_SIZE, SEEK_CUR)
-                || fread(ftyp_atom, atom_size, 1, infile) != 1) {
+                || fread(ftyp_atom, atom_size, 1, infile) != 1
+                || (start_offset = ftello(infile))<0) {
                 perror(argv[1]);
                 goto error_out;
             }
-            start_offset = ftello(infile);
         } else {
             int ret;
             /* 64-bit special case */