lib.sh: initialise PATH if it's unset

it's incorrect for PATH not to be set, but some users
may foolishly blank it out before running lbmk.

prevent such issues, by initialising it.

Signed-off-by: Leah Rowe <leah@libreboot.org>

include/lib.sh

@@ -6,6 +6,8 @@
 export LC_COLLATE=C
 export LC_ALL=C
 
+[ -z "${PATH+x}" ] && \
+    export PATH="/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games"
 xbmkpath="$PATH"
 
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