lavc/options_table: force non-negative bitrate range

It does not make sense to set a negative bitrate.

libavcodec/options_table.h

@@ -42,8 +42,8 @@
 #define AV_CODEC_DEFAULT_BITRATE 200*1000
 
 static const AVOption options[]={
-{"b", "set bitrate (in bits/s)", OFFSET(bit_rate), AV_OPT_TYPE_INT, {.i64 = AV_CODEC_DEFAULT_BITRATE }, INT_MIN, INT_MAX, A|V|E},
-{"ab", "set bitrate (in bits/s)", OFFSET(bit_rate), AV_OPT_TYPE_INT, {.i64 = 128*1000 }, INT_MIN, INT_MAX, A|E},
+{"b", "set bitrate (in bits/s)", OFFSET(bit_rate), AV_OPT_TYPE_INT, {.i64 = AV_CODEC_DEFAULT_BITRATE }, 0, INT_MAX, A|V|E},
+{"ab", "set bitrate (in bits/s)", OFFSET(bit_rate), AV_OPT_TYPE_INT, {.i64 = 128*1000 }, 0, INT_MAX, A|E},
 {"bt", "Set video bitrate tolerance (in bits/s). In 1-pass mode, bitrate tolerance specifies how far "
        "ratecontrol is willing to deviate from the target average bitrate value. This is not related "
        "to min/max bitrate. Lowering tolerance too much has an adverse effect on quality.",