avfilter/af_pan: Fix sscanf() use

Fixes: Memory Data Leak

Found-by: Simcha Kosman <simcha.kosman@cyberark.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavfilter/af_pan.c

@@ -196,7 +196,7 @@ static av_cold int init(AVFilterContext *ctx)
         sign = 1;
         while (1) {
             gain = 1;
-            if (sscanf(arg, "%lf%n *%n", &gain, &len, &len))
+            if (sscanf(arg, "%lf%n *%n", &gain, &len, &len) >= 1)
                 arg += len;
             if (parse_channel_name(&arg, &in_ch_id, &named)){
                 av_log(ctx, AV_LOG_ERROR,