libc: Reset the read buffer even when read() returns an error

This fixes the same data being read multiple times if an error was returned

libc/src/stdio.cpp

@@ -135,6 +135,8 @@ static ssize_t read_data_into_buffer(FILE* stream)
     stream->_buf.index = 0;
     ssize_t nread = read(stream->_fd, stream->_buf.buffer, stream->_buf.capacity);
     if (nread >= 0) stream->_buf.size = nread;
+    else
+        stream->_buf.size = 0;
     stream->_buf.status |= FileStatusFlags::LastRead;
     return nread;
 }