Cleanup: Font, added initialisation for two variables

My compiler (GCC 7.5.0) was warning about these variables potentially not
being initialised. Since the function is highly complex, instead of
analysing it I just trust my compiler and added initial values.

This should be no functional change.

source/blender/blenkernel/intern/font.c

@@ -734,7 +734,7 @@ static bool vfont_to_curve(Object *ob,
   float twidth = 0, maxlen = 0;
   int i, slen, j;
   int curbox;
-  int selstart, selend;
+  int selstart = 0, selend = 0;
   int cnr = 0, lnr = 0, wsnr = 0;
   const char32_t *mem = NULL;
   char32_t ascii;