[lldb] Fix type lookup in DWARF .o files via debug map (#87177)

An inverted condition causes `SymbolFileDWARFDebugMap::FindTypes` to
bail out after inspecting the first .o file in each module.

The same kind of bug is found in
`SymbolFileDWARFDebugMap::ParseDeclsForContext`.

Correct both early exit conditions and add a regression test for lookup
of up a type defined in a secondary compilation unit.

Fixes #87176