avcodec/h2645_parse: Avoid EAGAIN

EAGAIN causes an assertion failure when it is returned from the decoder

Fixes: Assertion consumed != (-(11)) failed at libavcodec/decode.c:462
Fixes: assertion_IOT_instruction_decode_c_462/poc

Found-by: Hardik Shah of Vehere (Dawn Treaders team)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 5ddab49d48)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/h2645_parse.h

@@ -123,7 +123,7 @@ static inline int get_nalsize(int nal_length_size, const uint8_t *buf,
 
     if (*buf_index >= buf_size - nal_length_size) {
         // the end of the buffer is reached, refill it
-        return AVERROR(EAGAIN);
+        return AVERROR_INVALIDDATA;
     }
 
     for (i = 0; i < nal_length_size; i++)