In fast completion scenario, 'AbstractFunctionDecl' may have the body
from the different file than the decl itself. Thay may confuses source
range checking.
As a workaround, always look into decls regardless of the range. This
should not regress the speed of the searching much because
statements/expressions (including nested function bodies) in the decl
is still skipped if it's outside the range.
rdar://problem/58098222
