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>
diff --git a/tools/genboardscfg.py b/tools/genboardscfg.py
index e92e4f8..f179803 100755
--- a/tools/genboardscfg.py
+++ b/tools/genboardscfg.py
@@ -142,7 +142,7 @@
                             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 = []