meson: enable -Wunterminated-string-initialization

With af1a6db58f, now we can build with the
option.

meson.build

@@ -399,6 +399,7 @@ possible_common_cc_flags = [
         '-Wstrict-aliasing=2',
         '-Wstrict-prototypes',
         '-Wsuggest-attribute=noreturn',
+        '-Wunterminated-string-initialization',
         '-Wunused-function',
         '-Wwrite-strings',
         '-Wzero-length-bounds',