cocci: use strempty() at more places

This shortens the code by a few lines.

src/basic/fileio.c

@@ -1225,8 +1225,7 @@ int tempfn_xxxxxx(const char *p, const char *extra, char **ret) {
         if (!filename_is_valid(fn))
                 return -EINVAL;
 
-        if (!extra)
-                extra = "";
+        extra = strempty(extra);
 
         t = new(char, strlen(p) + 2 + strlen(extra) + 6 + 1);
         if (!t)
@@ -1259,8 +1258,7 @@ int tempfn_random(const char *p, const char *extra, char **ret) {
         if (!filename_is_valid(fn))
                 return -EINVAL;
 
-        if (!extra)
-                extra = "";
+        extra = strempty(extra);
 
         t = new(char, strlen(p) + 2 + strlen(extra) + 16 + 1);
         if (!t)
@@ -1300,8 +1298,7 @@ int tempfn_random_child(const char *p, const char *extra, char **ret) {
                         return r;
         }
 
-        if (!extra)
-                extra = "";
+        extra = strempty(extra);
 
         t = new(char, strlen(p) + 3 + strlen(extra) + 16 + 1);
         if (!t)

src/basic/string-util.h

@@ -52,15 +52,15 @@ static inline bool streq_ptr(const char *a, const char *b) {
 }
 
 static inline const char* strempty(const char *s) {
-        return s ? s : "";
+        return s ?: "";
 }
 
 static inline const char* strnull(const char *s) {
-        return s ? s : "(null)";
+        return s ?: "(null)";
 }
 
 static inline const char *strna(const char *s) {
-        return s ? s : "n/a";
+        return s ?: "n/a";
 }
 
 static inline bool isempty(const char *p) {