avformat/nutdec: Fix use of uinitialized value

Fixes CID1041175

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 56abf35151c635caa3eb04bbb90454bae5463a09)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/nutdec.c

@@ -540,6 +540,8 @@ static int decode_info_header(NUTContext *nut)
             return ret;
         }
         value = get_s(bc);
+        str_value[0] = 0;
+
         if (value == -1) {
             type = "UTF-8";
             get_str(bc, str_value, sizeof(str_value));