get_bits: Add OPEN_READER macro variant w/o size_plus8

This avoids a trillion warnings from MSVC.

libavcodec/dvdec.c

@@ -88,7 +88,7 @@ static void dv_decode_ac(GetBitContext *gb, BlockInfo *mb, int16_t *block)
     int partial_bit_count = mb->partial_bit_count;
     int level, run, vlc_len, index;
 
-    OPEN_READER(re, gb);
+    OPEN_READER_NOSIZE(re, gb);
     UPDATE_CACHE(re, gb);
 
     /* if we must parse a partial VLC, we do it here */

libavcodec/get_bits.h

@@ -123,17 +123,18 @@ typedef struct RL_VLC_ELEM {
 #   define MIN_CACHE_BITS 25
 #endif
 
-#if UNCHECKED_BITSTREAM_READER
-#define OPEN_READER(name, gb)                   \
+#define OPEN_READER_NOSIZE(name, gb)            \
     unsigned int name ## _index = (gb)->index;  \
     unsigned int av_unused name ## _cache = 0
 
+#if UNCHECKED_BITSTREAM_READER
+#define OPEN_READER(name, gb) OPEN_READER_NOSIZE(name, gb)
+
 #define BITS_AVAILABLE(name, gb) 1
 #else
 #define OPEN_READER(name, gb)                   \
-    unsigned int name ## _index = (gb)->index;  \
-    unsigned int av_unused name ## _cache = 0;  \
-    unsigned int av_unused name ## _size_plus8 = (gb)->size_in_bits_plus8
+    OPEN_READER_NOSIZE(name, gb);               \
+    unsigned int name ## _size_plus8 = (gb)->size_in_bits_plus8
 
 #define BITS_AVAILABLE(name, gb) name ## _index < name ## _size_plus8
 #endif
@@ -254,7 +255,7 @@ static inline unsigned int get_bits(GetBitContext *s, int n)
 static inline unsigned int show_bits(GetBitContext *s, int n)
 {
     register int tmp;
-    OPEN_READER(re, s);
+    OPEN_READER_NOSIZE(re, s);
     UPDATE_CACHE(re, s);
     tmp = SHOW_UBITS(re, s, n);
     return tmp;