fix errors flagged by clang static analyzer

builtin.c: bug - free of uninitialized jv
compile.c: missing assertion
jq_test.c: buggy logic / unreachable code
jv.c: missing assertion
jv_alloc.c: false positive - intentional read of uninitialized memory
jv_file.c: dead code

jv_file.c

@@ -33,7 +33,6 @@ jv jv_load_file(const char* filename, int raw) {
       if (jv_invalid_has_msg(jv_copy(value))) {
         jv_free(data);
         data = value;
-        value = jv_invalid();
         break;
       }
     }