Correct stat() error check in decomposition library loading

The original code incorrectly used !stat() which would continue the loop
when the library was failed to be loaded (stat returns 0). Change to
continue searching for the library when stat() returns a non-zero.
Otherwise, an error message is reported.

ldms/src/ldmsd/ldmsd_decomp.c

@@ -125,7 +125,7 @@ static ldmsd_decomp_t decomp_get(const char *decomp, ldmsd_req_ctxt_t reqc)
 		d = dlopen(library_name, RTLD_NOW);
 		if (d)
 			break;
-		if (!stat(library_name, &st))
+		if (0 != stat(library_name, &st))
 			continue;
 		dlerr = dlerror();
 		errno = ELIBBAD;