command: define-section with empty contents removes a section

DOCS/man/input.rst

@@ -521,6 +521,8 @@ Input Commands that are Possibly Subject to Change
     ``input.conf`` file (except that using the section syntax in it is not
     allowed), including the need to separate bindings with a newline character.
 
+    If the ``contents`` parameter is an empty string, the section is removed.
+
     The section with the name ``default`` is the normal input section.
 
     In general, input sections have to be enabled with the ``enable-section``

input/input.c

@@ -1016,7 +1016,7 @@ void mp_input_define_section(struct input_ctx *ictx, char *name, char *location,
     // Delete:
     struct cmd_bind_section *bs = get_bind_section(ictx, bstr0(name));
     remove_binds(bs, builtin);
-    if (contents) {
+    if (contents && contents[0]) {
         // Redefine:
         parse_config(ictx, builtin, bstr0(contents), location, name);
     } else {