coccinelle: add reallocarray() coccinelle script

Let's systematically make use of reallocarray() whereever we invoke
realloc() with a product of two values.

src/shared/install.c

@@ -311,7 +311,7 @@ int unit_file_changes_add(
         if (!changes)
                 return 0;
 
-        c = realloc(*changes, (*n_changes + 1) * sizeof(UnitFileChange));
+        c = reallocarray(*changes, *n_changes + 1, sizeof(UnitFileChange));
         if (!c)
                 return -ENOMEM;
         *changes = c;

src/shared/uid-range.c

@@ -22,6 +22,7 @@
 #include <stdlib.h>
 #include <string.h>
 
+#include "alloc-util.h"
 #include "macro.h"
 #include "uid-range.h"
 #include "user-util.h"
@@ -109,7 +110,7 @@ int uid_range_add(UidRange **p, unsigned *n, uid_t start, uid_t nr) {
         } else {
                 UidRange *t;
 
-                t = realloc(*p, sizeof(UidRange) * (*n + 1));
+                t = reallocarray(*p, *n + 1, sizeof(UidRange));
                 if (!t)
                         return -ENOMEM;