Make sure to inizialize the r_error.error on Variant::construct

[AndreaCatania]

Make sure to initialize the r_error.error when Variant::construct is called.

The error passed to the function Variant::construct is not initialized: https://github.com/godotengine/godot/blob/master/modules/gdscript/gdscript_function.cpp#L958-L959

Since not all the constructors defined here: https://github.com/godotengine/godot/blob/master/core/variant/variant_construct.cpp#L738 always set r_error.error to something, happens that the error Bug, call error: #426275124 is raised with a random number, even when the function succeed.

Correct functions:

• https://github.com/godotengine/godot/blob/master/core/variant/variant_construct.cpp#L434-L437
• https://github.com/godotengine/godot/blob/master/core/variant/variant_construct.cpp#L399-L409
• https://github.com/godotengine/godot/blob/master/core/variant/variant_construct.cpp#L95-L108
• https://github.com/godotengine/godot/blob/master/core/variant/variant_construct.cpp#L66-L70
• ....

Bad functions:

• https://github.com/godotengine/godot/blob/master/core/variant/variant_construct.cpp#L341-L358
• https://github.com/godotengine/godot/blob/master/core/variant/variant_construct.cpp#L282-L299
• https://github.com/godotengine/godot/blob/master/core/variant/variant_construct.cpp#L224-L252
• https://github.com/godotengine/godot/blob/master/core/variant/variant_construct.cpp#L167-L195
• https://github.com/godotengine/godot/blob/master/core/variant/variant_construct.cpp#L133-L142
• ....

If we initialize the variable to CALL_OK, as I did in this PR, we can just leave the task to the above functions to set the error only when there is an error. In this way we can also make that mechanism less error prone and so more robust. Though, not sure if you would like to also set CALL_OK into those functions, or just leave them as are @reduz.

[vnen]

I believe we only need to initialize this in the CallError constructor (which is done among other things in #43730). This way we don't need to initialize on every call.

[AndreaCatania]

Yes, it works too.

[akien-mga]

Superseded by #43730.