BaseTools/Scripts/GetMaintainer: Simplify logic

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=4593

get_section_maintainers() either returns a list with
valid entries or an empty list.  It never returns None.
Simplify logic that accumulates maintainers and lists by
unconditionally appending lists returned from
get_section_maintainers().

Cc: Rebecca Cran <rebecca@bsdio.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Bob Feng <bob.c.feng@intel.com>
Cc: Yuwei Chen <yuwei.chen@intel.com>
Cc: Leif Lindholm <quic_llindhol@quicinc.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Acked-by: Rebecca Cran <rebecca@bsdio.com>
Reviewed-by: Leif Lindholm <quic_llindhol@quicinc.com>

BaseTools/Scripts/GetMaintainer.py

@@ -105,9 +105,7 @@ def get_maintainers(path, sections, level=0):
     lists = []
     for section in sections:
         tmp_maint, tmp_lists = get_section_maintainers(path, section)
-        if tmp_maint:
         maintainers += tmp_maint
-        if tmp_lists:
         lists += tmp_lists
 
     if not maintainers: