strv: fix STRV_FOREACH_PAIR macro definition

src/shared/strv.h

@@ -77,7 +77,7 @@ bool strv_overlap(char **a, char **b);
         for (; (l) && ((s) >= (l)); (s)--)
 
 #define STRV_FOREACH_PAIR(x, y, l)               \
-        for ((x) = (l), (y) = (x+1); (x) && *(x) && *(y); (x) += 2)
+        for ((x) = (l), (y) = (x+1); (x) && *(x) && *(y); (x) += 2, (y) = (x + 1))
 
 
 char **strv_sort(char **l);