avcodec/jpeglsdec: Check run value more completely in ls_decode_line()

previously it could have been by 1 too large
Fixes out of array access
Fixes: asan_heap-oob_12240f5_1_asan_heap-oob_12240f5_448_t8c1e3.jls
Fixes: asan_heap-oob_12240f5_1_asan_heap-oob_12240f5_448_t8nde0.jls
Fixes: asan_heap-oob_12240fa_1_asan_heap-oob_12240fa_448_t16e3.jls

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/jpeglsdec.c

@@ -269,6 +269,11 @@ static inline void ls_decode_line(JLSState *state, MJpegDecodeContext *s,
                 x += stride;
             }
 
+            if (x >= w) {
+                av_log(NULL, AV_LOG_ERROR, "run overflow\n");
+                return;
+            }
+
             /* decode run termination value */
             Rb     = R(last, x);
             RItype = (FFABS(Ra - Rb) <= state->near) ? 1 : 0;