Make --max-alloc=0 safer.

Always do size checking in my_alloc(), even for `--max-alloc=0`.

options.c

@@ -1946,6 +1946,8 @@ int parse_arguments(int *argc_p, const char ***argv_p)
 			goto cleanup;
 		max_alloc = size;
 	}
+	if (!max_alloc)
+		max_alloc = SIZE_MAX;
 
 	if (old_style_args < 0) {
 		if (!am_server && protect_args <= 0 && (arg = getenv("RSYNC_OLD_ARGS")) != NULL && *arg) {

rsync.1.md

@@ -2106,7 +2106,8 @@ expand it.
     See the [`--max-size`](#opt) option for a description of how SIZE can be
     specified.  The default suffix if none is given is bytes.
 
-    Beginning in 3.2.3, a value of 0 specifies no limit.
+    Beginning in 3.2.7, a value of 0 is an easy way to specify SIZE_MAX (the
+    largest limit possible).
 
     You can set a default value using the environment variable
     [`RSYNC_MAX_ALLOC`](#) using the same SIZE values as supported by this

util2.c

@@ -72,7 +72,7 @@ int msleep(int t)
 
 void *my_alloc(void *ptr, size_t num, size_t size, const char *file, int line)
 {
-	if (max_alloc && num >= max_alloc/size) {
+	if (num >= max_alloc/size) {
 		if (!file)
 			return NULL;
 		rprintf(FERROR, "[%s] exceeded --max-alloc=%s setting (file=%s, line=%d)\n",