Fix the table lookup in the perl script that checks all tables

When moving to relative paths in the test suite the perl script that
runs lou_checktable on all tables was apparently forgotten. So
basically it checked no table anymore. This should hopefully fix this.

tests/check_all_tables.pl

@@ -17,10 +17,11 @@
 # some tables are quite big and take some time to check, so keep the timeout reasonably long
 my $timeout = 120; # seconds
 
-# We assume that the productive tables, i.e. the ones that are shipped
-# with liblouis (and need to be tested) are found in the first path in
-# LOUIS_TABLEPATH. The subsequent entries are for test tables.
-my $tablesdir = (split(',', $ENV{LOUIS_TABLEPATH}))[0];
+# In the test suite the LOUIS_TABLEPATH is set up so that it actually
+# points at the top src dir of liblouis. So to find the productive
+# tables, i.e. the ones that are shipped with liblouis (and need to be
+# tested) we have to check the tables subdir.
+my $tablesdir = "$ENV{LOUIS_TABLEPATH}/tables";
 
 # get all the tables from the tables directory
 my @tables = glob("$tablesdir/*.{utb,ctb,tbl}");