tools/genboardscfg.py: fix a bug of MAINTAINERS handling

This patch fixes a minor problem:
If a block without "F:   configs/*_defconfig" is followed by another
block with "F:   configs/*_defconfig", the maintainers from the
former block are squashed into the latter.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>

tools/genboardscfg.py

@@ -142,7 +142,7 @@ class MaintainersDatabase:
                             targets.append(front)
             elif tag == 'S:':
                 status = rest
-            elif line == '\n' and targets:
+            elif line == '\n':
                 for target in targets:
                     self.database[target] = (status, maintainers)
                 targets = []