basic: make check-pointer-deref clean

Add the needed assert changes to make the code clean
for the new check-pointer-deref script.

Note that for `_cmp()` functions its a bit of a question
if we want `assert()` or `POINTER_MAY_BE_NULL()` here. The
former is more correct but it adds a (small) runtime hit. If
we use POINTER_MAY_BE_NULL() it is compiled out but strictly
speaking it is wrong (so at least we would need a comment).

src/basic/parse-util.c

@@ -127,6 +127,8 @@ int parse_mtu(int family, const char *s, uint32_t *ret) {
         uint64_t u, m;
         int r;
 
+        assert(ret);
+
         r = parse_size(s, 1024, &u);
         if (r < 0)
                 return r;
@@ -376,6 +378,9 @@ int parse_user_shell(const char *s, char **ret_sh, bool *ret_copy) {
         char *sh;
         int r;
 
+        assert(ret_sh);
+        assert(ret_copy);
+
         if (path_is_absolute(s) && path_is_normalized(s)) {
                 sh = strdup(s);
                 if (!sh)
@@ -476,6 +481,8 @@ int safe_atou_bounded(const char *s, unsigned min, unsigned max, unsigned *ret)
         unsigned v;
         int r;
 
+        assert(ret);
+
         r = safe_atou(s, &v);
         if (r < 0)
                 return r;
@@ -577,6 +584,8 @@ int safe_atou8_full(const char *s, unsigned base, uint8_t *ret) {
         unsigned u;
         int r;
 
+        assert(ret);
+
         r = safe_atou_full(s, base, &u);
         if (r < 0)
                 return r;
@@ -591,6 +600,8 @@ int safe_atou16_full(const char *s, unsigned base, uint16_t *ret) {
         unsigned u;
         int r;
 
+        assert(ret);
+
         r = safe_atou_full(s, base, &u);
         if (r < 0)
                 return r;
@@ -654,6 +665,9 @@ int parse_fractional_part_u(const char **p, size_t digits, unsigned *res) {
         unsigned val = 0;
         const char *s;
 
+        assert(p);
+        assert(res);
+
         s = *p;
 
         /* accept any number of digits, strtoull is limited to 19 */
@@ -688,6 +702,8 @@ int parse_fractional_part_u(const char **p, size_t digits, unsigned *res) {
 int parse_nice(const char *s, int *ret) {
         int n, r;
 
+        assert(ret);
+
         r = safe_atoi(s, &n);
         if (r < 0)
                 return r;
@@ -703,6 +719,8 @@ int parse_ip_port(const char *s, uint16_t *ret) {
         uint16_t l;
         int r;
 
+        assert(ret);
+
         r = safe_atou16_full(s, SAFE_ATO_REFUSE_LEADING_WHITESPACE, &l);
         if (r < 0)
                 return r;
@@ -719,6 +737,9 @@ int parse_ip_port_range(const char *s, uint16_t *low, uint16_t *high, bool allow
         unsigned l, h;
         int r;
 
+        assert(low);
+        assert(high);
+
         r = parse_range(s, &l, &h);
         if (r < 0)
                 return r;