avformat/flvdec: Increase string array size

Fixes parsing httphostheader of Scarlatti\,\ Pieter-Jan\ Belder\ -\ Sonata\ K113\ in\ A\ major\ -\ Alle.flv
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit eb767a27)
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/flvdec.c

@@ -390,7 +390,7 @@ static int amf_parse_object(AVFormatContext *s, AVStream *astream,
     FLVContext *flv = s->priv_data;
     AVIOContext *ioc;
     AMFDataType amf_type;
-    char str_val[256];
+    char str_val[1024];
     double num_val;
 
     num_val  = 0;