kpress function in x.c previously relied on the wrong understanding
of XmbLookupString behavior. When the composed string is longer
than the available buffer, the buffer is not initialized and the
actual length of the data available to read is returned, not
the amount of data written. When that amount is later used to
process the contents of this buffer, not only will the random
contents of the uninitialized buffer be sent directly to the
terminal and whichever application is now running in it, but
possibly also whatever is in the memory after that buffer,
leading to undefined behavior and possible random command execution.