Fix crash on 64bit platforms in change_mem2()
https://bugs.gentoo.org/753950

From upstream:
https://sourceforge.net/p/ucon64/svn/2821/
--- a/libdiscmage/misc.c
+++ b/libdiscmage/misc.c
@@ -1875,5 +1875,5 @@
           if (strpos == pos_1st_esc)
             setindex = 0;                       // reset argument pointer
-          if (pos_1st_esc == (unsigned int) -1)
+          if (pos_1st_esc == (size_t) -1)
             pos_1st_esc = strpos;
 
--- a/misc/misc.c
+++ b/misc/misc.c
@@ -502,5 +502,5 @@
           if (strpos == pos_1st_esc)
             setindex = 0;                       // reset argument pointer
-          if (pos_1st_esc == (unsigned int) -1)
+          if (pos_1st_esc == (size_t) -1)
             pos_1st_esc = strpos;