Rewrite exit_if_paths_do_not_exist to not check files multiple times.

diffoscope/utils.py

@@ -56,12 +56,17 @@ def format_bytes(size, decimal_places=2):
 
 
 def exit_if_paths_do_not_exist(*paths):
-    if not all(map(os.path.lexists, paths)):
-        for path in paths:
-            if not os.path.lexists(path):
-                sys.stderr.write(
-                    "%s: %s: No such file or directory\n" % (sys.argv[0], path)
-                )
+    flag = False
+    for path in paths:
+        if os.path.lexists(path):
+            continue
+        flag = True
+        print(
+            f"{sys.argv[0]}: {path}: No such file or directory",
+            file=sys.stderr,
+        )
+
+    if flag:
         sys.exit(2)