Clippy: mutable borrow from immutable input

[kakserpom]

Following up on #460.
I need the collective mind's assistance.

Here are the remaining Clippy errors.

    Checking ext-php-rs v0.13.1
error: mutable borrow from immutable input(s)
   --> src/types/array.rs:219:51
    |
219 |     pub fn get_mut(&self, key: &'_ str) -> Option<&mut Zval> {
    |                                                   ^^^^^^^^^
    |
note: immutable borrow here
   --> src/types/array.rs:219:20
    |
219 |     pub fn get_mut(&self, key: &'_ str) -> Option<&mut Zval> {
    |                    ^^^^^
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#mut_from_ref
    = note: `#[deny(clippy::mut_from_ref)]` on by default

error: mutable borrow from immutable input(s)
   --> src/types/array.rs:274:53
    |
274 |     pub fn get_index_mut(&self, key: u64) -> Option<&mut Zval> {
    |                                                     ^^^^^^^^^
    |
note: immutable borrow here
   --> src/types/array.rs:274:26
    |
274 |     pub fn get_index_mut(&self, key: u64) -> Option<&mut Zval> {
    |                          ^^^^^
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#mut_from_ref

error: mutable borrow from immutable input(s)
   --> src/types/class_object.rs:176:60
    |
176 |     fn internal_from_zend_obj(std: &zend_object) -> Option<&mut Self> {
    |                                                            ^^^^^^^^^
    |
note: immutable borrow here
   --> src/types/class_object.rs:176:36
    |
176 |     fn internal_from_zend_obj(std: &zend_object) -> Option<&mut Self> {
    |                                    ^^^^^^^^^^^^
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#mut_from_ref

error: mutable borrow from immutable input(s)
   --> src/types/zval.rs:265:42
    |
265 |     pub fn indirect_mut(&self) -> Option<&mut Zval> {
    |                                          ^^^^^^^^^
    |
note: immutable borrow here
   --> src/types/zval.rs:265:25
    |
265 |     pub fn indirect_mut(&self) -> Option<&mut Zval> {
    |                         ^^^^^
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#mut_from_ref

error: mutable borrow from immutable input(s)
   --> src/zend/class.rs:115:76
    |
115 |     pub fn get_iterator<'a>(&self, zval: &'a Zval, by_ref: bool) -> Option<&'a mut ZendIterator> {
    |                                                                            ^^^^^^^^^^^^^^^^^^^^
    |
note: immutable borrow here
   --> src/zend/class.rs:115:42
    |
115 |     pub fn get_iterator<'a>(&self, zval: &'a Zval, by_ref: bool) -> Option<&'a mut ZendIterator> {
    |                                          ^^^^^^^^
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#mut_from_ref

error: mutable borrow from immutable input(s)
   --> src/zend/globals.rs:109:48
    |
109 |     pub fn function_table_mut(&self) -> Option<&mut ZendHashTable> {
    |                                                ^^^^^^^^^^^^^^^^^^
    |
note: immutable borrow here
   --> src/zend/globals.rs:109:31
    |
109 |     pub fn function_table_mut(&self) -> Option<&mut ZendHashTable> {
    |                               ^^^^^
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#mut_from_ref

[Xenira]

Just stumbled over this as well. Will allow it, but keep this issue to verify this is safe. We might need to change the method signature to require a &mut self.