Client: Convert UsernameValidator line separators from CRLF to LF

All other files in the client project use LF line endings.
Done with `find client -type f | xargs dos2unix`

client/src/main/java/com/aapeli/multiuser/UsernameValidator.java

@@ -1,13 +1,13 @@
-package com.aapeli.multiuser;
-
-import java.util.regex.Pattern;
-
-public class UsernameValidator {
-    public static Pattern INVALID_VALID_USERNAME_PATTERN = Pattern.compile("[^a-zA-Z0-9 ]");
-
-    public static boolean isValidUsername(String username) {
-        boolean invalid = INVALID_VALID_USERNAME_PATTERN.matcher(username).find() || username.trim().isEmpty();
-        return !invalid;
-
-    }
-}
+package com.aapeli.multiuser;
+
+import java.util.regex.Pattern;
+
+public class UsernameValidator {
+    public static Pattern INVALID_VALID_USERNAME_PATTERN = Pattern.compile("[^a-zA-Z0-9 ]");
+
+    public static boolean isValidUsername(String username) {
+        boolean invalid = INVALID_VALID_USERNAME_PATTERN.matcher(username).find() || username.trim().isEmpty();
+        return !invalid;
+
+    }
+}