add an explicit conversion from size_t to int

Function ans_read_int() takes int as parameter, this commit uses an
explicit conversion to avoid MSVC building warning.

Change-Id: Ia405e1d5a86c0f42932fa1da29417ccbf2dd58e7

av1/decoder/decodeframe.c

diff --git a/av1/decoder/decodeframe.c b/av1/decoder/decodeframe.c
index 1f1f358..638fa01 100644
--- a/av1/decoder/decodeframe.c
+++ b/av1/decoder/decodeframe.c
@@ -3478,7 +3478,7 @@
     aom_internal_error(&cm->error, AOM_CODEC_MEM_ERROR,
                        "Failed to allocate bool decoder 0");
 #else
-  if (ans_read_init(&r, data, partition_size))
+  if (ans_read_init(&r, data, (int)partition_size))
     aom_internal_error(&cm->error, AOM_CODEC_MEM_ERROR,
                        "Failed to allocate compressed header ANS decoder");
 #endif  // !CONFIG_ANS