Properly handle embedded nul delimited string lists

For example:

reserved-names="res1\0res2\0res3";

Where \0 is an actual embedded NUL in the source instead of a string
escape. To achieve this, use the len given by the lexer instead of
strlen.

Without this patch dtc will mangle the output and possibly hang on
realloc.
diff --git a/tests/run_tests.sh b/tests/run_tests.sh
index f94d361..ace6e4f 100755
--- a/tests/run_tests.sh
+++ b/tests/run_tests.sh
@@ -275,6 +275,10 @@
     run_dtc_test -I dts -O dtb -o sourceoutput.test.dtb sourceoutput.dts
     run_dtc_test -I dts -O dtb -o sourceoutput.test.dts.test.dtb sourceoutput.test.dts
     run_test dtbs_equal_ordered sourceoutput.test.dtb sourceoutput.test.dts.test.dtb
+
+    run_dtc_test -I dts -O dtb -o embedded_nul.test.dtb embedded_nul.dts
+    run_dtc_test -I dts -O dtb -o embedded_nul_equiv.test.dtb embedded_nul_equiv.dts
+    run_test dtbs_equal_ordered embedded_nul.test.dtb embedded_nul_equiv.test.dtb
 }
 
 dtc_tests () {