avfilter/vf_deshake_opencl: Ensure that the first iteration initializes the best variables

Fixes: CID1452759 Uninitialized scalar variable

Sponsored-by: Sovereign Tech Fund
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 9385847af4)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavfilter/vf_deshake_opencl.c

@@ -703,7 +703,7 @@ static int minimize_error(
             total_err += deshake_ctx->ransac_err[j];
         }
 
-        if (total_err < best_err) {
+        if (i == 0 || total_err < best_err) {
             for (int mi = 0; mi < 6; ++mi) {
                 best_model[mi] = model[mi];
             }