Fix json buffer reallocation issue

Instead of try to guess if we will need more space for future inserions,
wait for exhaustion and allocate twice the required space. This is far from perfect
but works better. Now Json output works all the time.

dump1090.c

@@ -2175,13 +2175,18 @@ char *aircraftsToJson(int *len) {
                 a->reg?a->reg->code:"",
                 a->flight, a->lat, a->lon, a->altitude, a->track,
                 a->speed);
-            p += l; buflen -= l;
+
             /* Resize if needed. */
-            if (buflen < 256) {
+	    if (l >= buflen) {
 		int used = p-buf;
-                buflen += 1024; /* Our increment. */
+		buflen += (2*l); /* Our increment. */
 		buf = realloc(buf,used+buflen);
+		if (buf == NULL) exit(1);
 		p = buf+used;
+		/* try to add the current airplane again */
+		continue;
+	    } else {
+		p += l; buflen -= l;
             }
         }
         a = a->next;