fix(gnovm): fix nil pointer deref for duplicate declarations

[ltzmaxwell]

close: #2763 .

This PR addresses the nil pointer issue, also fix the redeclaration issue by @thehowl .
filetest is a special case, , redeclaration is still permitted in filetest files(e.g. z_0_filetest, z_1_filetest...) for convenience.

[Gno2D2]

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[notJoon]

Nice. I confirmed that there is no nil pointer issue. 👍

Personally, I think it would be good to check for redeclarations, but I also agree that adding a separate check for such this cases would be inefficient. However, this seems to be beyond my hand, so I'll let it go.

[thehowl]

I'll fix this up a second (adding more tests)

[ltzmaxwell]

thanks @thehowl for the fix, it's elegant and concise. 👍

[thehowl]

@ltzmaxwell does the txtar in gno.land make sense in your opinion - or should we remove it? i think it's not testing anything in particular, because test files aren't considered

[ltzmaxwell]

@ltzmaxwell does the txtar in gno.land make sense in your opinion - or should we remove it? i think it's not testing anything in particular, because test files aren't considered

IMO, it serves as a helpful explanation after adding this part of the clarification:

# Note: addpkg does not add *_test.gno files, so it works as expected without
# causing any redeclaration issues.

@thehowl