avcodec/jpeg2000dwt: Fix left shift of negative number

Fixes the j2k-dwt FATE-test; also fixes #9945.
(I don't know whether the multiplication can overflow.)
Reviewed-by: Tomas Härdin <git@haerdin.se>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/jpeg2000dwt.c

@@ -81,7 +81,7 @@ static void sd_1d53(int *p, int i0, int i1)
 
     if (i1 <= i0 + 1) {
         if (i0 == 1)
-            p[1] <<= 1;
+            p[1] *= 2;
         return;
     }