[core] Complement OpenURL implementation for SDL

[ghost]

Changes

1. Complements OpenURL missing the avoid [\'] character check (L1018) on rcore_desktop_sdl.c (R902-R904). And also the security warning (R896-R899).

Environment

Changes tested on Linux (Mint 21.1 64-bit).

Edits

1: added line marks.

[ghost]

@raysan5 Perhaps it would be a good idea to also add the security warning (R896-R899) to the cheatsheet/ raylib.h (L1062).

[raysan5]

@ubkp thanks for the review! Actually, I did not implement it because I didn't know if it could be managed by SDL_OpenURL internally, but it seems it's up to the user.

[ghost]

@raysan5 Sorry to ask again, but do you think the security warning (R896-R899) should be added the cheatsheet/ raylib.h (L1062) too? It looks important.

[raysan5]

@ubkp I prefer to avoid those long comments in the cheatsheets, maybe it can be simplified to just "basic URL security checks" at the end or no need to add it. In any case, if a inappropiate url is provided a tracelog message is shown.