[calls] util: Add STR_IS_NULL_OR_EMPTY macro

[Evangelos Ribeiro Tzaras <devrtz src gnome org>]

commit 53129e92af3d863e6951b521f3d49f5c88563ada
Author: Evangelos Ribeiro Tzaras <devrtz fortysixandtwo eu>
Date:   Fri Feb 18 09:23:39 2022 +0100

    util: Add STR_IS_NULL_OR_EMPTY macro
    
    Shamelessly copied from
    https://gitlab.gnome.org/World/Phosh/phosh/-/blob/main/src/util.h#L13

 src/util.h | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/src/util.h b/src/util.h
index d2256457..4aa2d0a7 100644
--- a/src/util.h
+++ b/src/util.h
@@ -28,6 +28,8 @@
 
 G_BEGIN_DECLS
 
+#define STR_IS_NULL_OR_EMPTY(x) ((x) == NULL || (x)[0] == '\0')
+
 /*
  * For defining simple interface functions
  */