avcodec/put_bits: Always check buffer end before writing

This causes a overall slowdown of 0.1 % (tested with mpeg4 single thread encoding of matrixbench at QP=3)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/put_bits.h

@@ -163,9 +163,13 @@ static inline void put_bits(PutBitContext *s, int n, unsigned int value)
 #ifdef BITSTREAM_WRITER_LE
     bit_buf |= value << (32 - bit_left);
     if (n >= bit_left) {
-        av_assert2(s->buf_ptr+3<s->buf_end);
+        if (3 < s->buf_end - s->buf_ptr) {
             AV_WL32(s->buf_ptr, bit_buf);
             s->buf_ptr += 4;
+        } else {
+            av_log(NULL, AV_LOG_ERROR, "Internal error, put_bits buffer too small\n");
+            av_assert2(0);
+        }
         bit_buf     = value >> bit_left;
         bit_left   += 32;
     }
@@ -177,9 +181,13 @@ static inline void put_bits(PutBitContext *s, int n, unsigned int value)
     } else {
         bit_buf   <<= bit_left;
         bit_buf    |= value >> (n - bit_left);
-        av_assert2(s->buf_ptr+3<s->buf_end);
+        if (3 < s->buf_end - s->buf_ptr) {
             AV_WB32(s->buf_ptr, bit_buf);
             s->buf_ptr += 4;
+        } else {
+            av_log(NULL, AV_LOG_ERROR, "Internal error, put_bits buffer too small\n");
+            av_assert2(0);
+        }
         bit_left   += 32 - n;
         bit_buf     = value;
     }