Ensure instance name is a valid Windows file name

Add check for instance name that ensures it being a valid Windows file.
See the microsoft article about naming files for more details:
https://docs.microsoft.com/en-us/windows/win32/fileio/naming-a-file

test/client.js

@@ -19,6 +19,58 @@ describe("Client testing", function() {
 		})
 	});
 
+	describe("checkFilename()", function() {
+		it("should allow a basic name", function() {
+			client._checkFilename("file");
+		});
+
+		function check(item, msg) {
+			assert.throws(() => client._checkFilename(item), new Error(msg));
+		}
+
+		it("should throw on non-string", function() {
+			check(undefined, "must be a string");
+			check(null, "must be a string");
+			check({}, "must be a string");
+			check([], "must be a string");
+			check(0, "must be a string");
+			check(false, "must be a string");
+		});
+
+		it("should throw on empty name", function() {
+			check("", "cannot be empty");
+		});
+
+		it("should throw on <>:\"\\/|?* \\x00\\r\\n\\t", function() {
+			for (let char of '<>:"\\/|?*\x00\r\n\t') {
+				check(char, 'cannot contain <>:"\\/|=* or control characters');
+			}
+		});
+
+		it("should throw on CON, PRN, AUX, NUL, COM1, LPT1", function() {
+			for (let bad of ['CON', 'PRN', 'AUX', 'NUL', 'COM1', 'LPT1']) {
+				check(
+					bad, 'cannot be named any of . ..'
+					+' CON PRN AUX NUL COM1-9 and LPT1-9'
+				);
+			}
+		});
+
+		it("should throw on . and ..", function() {
+			for (let bad of ['.', '..']) {
+				check(
+					bad, 'cannot be named any of . ..'
+					+' CON PRN AUX NUL COM1-9 and LPT1-9'
+				);
+			}
+		});
+
+		it("should throw on names ending with . or space", function() {
+			check("a ", "cannot end with . or space");
+			check("a.", "cannot end with . or space");
+		});
+	});
+
 	describe("randomDynamicPort()", function() {
 		it("should return a port number", function() {
 			let port = client._randomDynamicPort()