Added test case when field was already hitted

src/main/java/de/tims/fleetstorm/matchfield/Coordinate.java

@@ -45,7 +45,7 @@ public class Coordinate {
 	}
 
 	public boolean shoot() {
-		if (this.state == Coordinate.SHOT)
+		if (this.state == Coordinate.SHOT || this.state == Coordinate.HIT)
 			return false;
 
 		if (this.state == Coordinate.SHIP) {

src/test/java/de/tims/fleetstorm/matchfield/CoordinateTest.java

@@ -76,6 +76,9 @@ class CoordinateTest {
 
 		assertTrue(matchfield.getField(0, 0).shoot());
 		assertFalse(matchfield.getField(0, 0).shoot());
+
+		matchfield.getField(3, 4).shoot();
+		assertFalse(matchfield.getField(3, 4).shoot());
 	}
 
 }