HELP: Apply local patch in phase

[phodina via <help-guix@gnu.org>]

Hello,

could you please suggest how to apply local patch using gexp?

The reason the patch is not applied to source is that it patches code from submodule which is downloaded after unpack phase finishes.

There's nice example in the file 'gnu/packages/games.scm'

Here we list the patch as dependency:
```
(native-inputs
`(("unzip" ,unzip)
("patch" ,patch) ("love-11.patch" ,(search-patch "mrrescue-support-love-11.patch"))))
```
Here's transformation to inputs without labels for my case:
```
(native-inputs
`(("unzip" ,unzip)
("patch" ,patch) ("love-11.patch" ,(search-patch "mrrescue-support-love-11.patch"))))
```
And later we apply the patch:
```
(invoke patch "-p1" "-i"
(assoc-ref %build-inputs "love-11.patch")))
```
The issue here is when I attempt to do so with following code the expression returns #f as the patch is not found:
```
(invoke (search-input-file inputs "/bin/patch") "-p1" "-i" (search-input-file inputs "zenlib_dynamic_physfs.diff"))
```

Any ideas what to change?

----
Petr