lisb/str.c: simplify xtoi()

If str == ' ', str has to be non-zero. No extra check is needed.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

lib/str.c

@@ -274,7 +274,7 @@ xtoi (
     CHAR16      c;
 
     // skip preceeding white space
-    while (*str && *str == ' ') {
+    while (*str == ' ') {
         str += 1;
     }