stream: make eof flag more consistent

When reading something successfully, the eof flag should never be 1, so
clear it in these situations. The eof flag will be set properly on the
next read call.

stream/stream.c

@@ -432,6 +432,8 @@ int stream_read_partial(stream_t *s, char *buf, int buf_size)
     int len = FFMIN(buf_size, s->buf_len - s->buf_pos);
     memcpy(buf, &s->buffer[s->buf_pos], len);
     s->buf_pos += len;
+    if (len > 0)
+        s->eof = 0;
     return len;
 }
 
@@ -445,7 +447,10 @@ int stream_read(stream_t *s, char *mem, int total)
         mem += read;
         len -= read;
     }
-    return total - len;
+    total -= len;
+    if (total > 0)
+        s->eof = 0;
+    return total;
 }
 
 // Read ahead at most len bytes without changing the read position. Return a