include/xalloc: ensure xstrdup() and xstrndup() returns nonnull attribute

Turned out lsblk is passing null as argument to xstrdup(), so fix that and
add assert() to make sure promise of not returning null is kept in future.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>

include/xalloc.h

@@ -62,8 +62,7 @@ static inline char __attribute__((warn_unused_result)) __ul_returns_nonnull
 {
         char *ret;
 
-        if (!str)
-                return NULL;
+        assert(str);
 
         ret = strdup(str);
 
@@ -77,8 +76,7 @@ xstrndup(const char *str, size_t size)
 {
         char *ret;
 
-        if (!str)
-                return NULL;
+        assert(str);
 
         ret = strndup(str, size);
 

misc-utils/lsblk.c

@@ -774,8 +774,14 @@ static char *device_get_data(
 		str = get_vfs_attribute(dev, id);
 		break;
 	case COL_TARGET:
-		str = xstrdup(lsblk_device_get_mountpoint(dev));
+	{
+		char *s = lsblk_device_get_mountpoint(dev);
+		if (s)
+			str = xstrdup(s);
+		else
+			str = NULL;
 		break;
+	}
 	case COL_LABEL:
 		prop = lsblk_device_get_properties(dev);
 		if (prop && prop->label)