[clang-warning-fix][dangling-else]

My last change to this file created some dangling elses that could be ambiguously parsed.
[clang-warning-fix][implicit-null-conversion]

Re-added after discussion at https://github.com/tpaviot/oce/commit/3cf60d6712b106c2680adbab8560d4d4b55821d4
[mingw-warning-fix][dangling-else]
[mingw-warning-fix][op-precedence]

Fixes -Wparentheses warning.

(nbSel1 == nbSel2 == 1) is evaluated as ((nbSel1 == nbSel2) == 1), so I'm not sure why that 1 is there in the first place.
[mingw-warning-fix][delete-void-pointer]

Deleting void* is undefined.