bug#21152: emacs make system blocked if "Xft/DPI = -1" in xsettings

[Xu Fasheng]

Hi, everyone.

I found that emacs could not compute a right dpi value if "Xft/DPI =
-1" in xsettings. The document said "Xft/DPI" is an integer, and "-1"
is the default value [1].

And in the code of src/xsettings.c:parse_settings(), all the interger
value in xsettings are converted to CARD32(unsigned int). So if
Xft/DPI is "-1", emacs will convert it to uint(4294967295), and owns a
huge dpi(4294967295/1024=4194303). Its so huge that will make system
blocked.

Here is the code snippets in
emacs24-24.5+1/src/xsettings.c:parse_settings() from debian/sid:
    ....
    420: CARD32 vlen, ival = 0;
    ....
    544: else if (strcmp (name, "Xft/DPI") == 0)
    545:  {
    546:    settings->seen |= SEEN_DPI;
    547:    settings->dpi = (double)ival/1024.0;
    548:  }

[1] http://www.freedesktop.org/wiki/Specifications/XSettingsRegistry/