Golang x/tools/go/analysis/passes/stringintconv: sometimes generates empty edits in suggested fixes

With https://go.dev/cl/592155 the stringintconv analyzer now generated sometimes suggested fixes with empty edits (if the fmt import already exists). This might break down stream tooling that tries to apply these edits because such tooling is not able to find the file with an empty path.

The analyzer should only generate an edit if is actually needed as it is not well defined what an empty edit means.

I prepared a fix in https://go.dev/cl/594258.

Comment From: joedian

Fix merged.