android: Escape backslashes in settings values

For usernames that use domain specifiers.

src/frontends/android/app/src/main/java/org/strongswan/android/utils/SettingsWriter.java

@@ -118,7 +118,7 @@ public class SettingsWriter
 	 */
 	private String escapeValue(String value)
 	{
-		return value.replace("\"", "\\\"");
+		return value.replace("\\", "\\\\").replace("\"", "\\\"");
 	}
 
 	/**

src/frontends/android/app/src/test/java/org/strongswan/android/test/SettingsWriterTest.java

@@ -95,7 +95,8 @@ public class SettingsWriterTest
 		SettingsWriter writer = new SettingsWriter();
 		writer.setValue("key", "val\"ue");
 		writer.setValue("nl", "val\nue");
-		assertEquals("serialized", "key=\"val\\\"ue\"\nnl=\"val\nue\"\n", writer.serialize());
+		writer.setValue("bs", "val\\ue");
+		assertEquals("serialized", "key=\"val\\\"ue\"\nnl=\"val\nue\"\nbs=\"val\\\\ue\"\n", writer.serialize());
 	}
 
 	@Test