Invalid UTF-8 strings

[Matt Bragano <maestro485 comcast net>]

I've been getting this series of error messages when displaying certain 
strings:

Pango-WARNING **: Invalid UTF-8 string passed to pango_layout_set_text()

I figured that the normalize() function might do the trick to get rid of 
these warnings, but when using normalize() the program crashes with this 
error:

glibmm-ERROR **:
unhandled exception (type std::exception) in signal handler:
what: attempt to create string with null pointer

aborting...
Aborted

Also, the strings in question are just standard Glib::ustrings, no old C 
strings or anything floating around.

Although the program behaves as expected when giving the pango warnings, 
I would rather fix whatever problem might exist to eliminate the 
warnings altogether.  Any advice?

Thanks,

Matt Bragano