tree-wide: avoid uninitialized warning on _cleanup_ variables

With some versions of the compiler, the _cleanup_ attr makes it think
the variable might be freed/closed when uninitialized, even though it
cannot happen. The added cost is small enough to be worth the benefit,
and optimized builds will help reduce it even further.

src/core/dbus-execute.c

@@ -1627,7 +1627,7 @@ int bus_exec_context_set_transient_property(
 
                                 unit_write_settingf(u, flags, name, "RootHash=");
                         } else {
-                                _cleanup_free_ void *p;
+                                _cleanup_free_ void *p = NULL;
 
                                 encoded = hexmem(roothash_decoded, roothash_decoded_size);
                                 if (!encoded)
@@ -1673,7 +1673,7 @@ int bus_exec_context_set_transient_property(
 
                                 unit_write_settingf(u, flags, name, "RootHashSignature=");
                         } else {
-                                _cleanup_free_ void *p;
+                                _cleanup_free_ void *p = NULL;
                                 ssize_t len;
 
                                 len = base64mem(roothash_sig_decoded, roothash_sig_decoded_size, &encoded);