Account for spacing in MapFont#getWidth(). Fixes BUKKIT-4089

Prior to this commit MapFont#getWidth() did not account for the 1px
spacing inserted by CraftMapCanvas#drawText().

This commit adds the consideration of the 1px spacing per character
while taking care to not consider the last character as it will not
have a 1px space behind it. This commit also ensures the method will
not check a 0-length String.

By: eueln <euelnd@gmail.com>

paper-api/src/main/java/org/bukkit/map/MapFont.java

@@ -52,10 +52,16 @@ public class MapFont {
             throw new IllegalArgumentException("text contains invalid characters");
         }
 
+        if (text.length() == 0){
+            return 0;
+        }
+
         int result = 0;
         for (int i = 0; i < text.length(); ++i) {
             result += chars.get(text.charAt(i)).getWidth();
         }
+        result += text.length() - 1; // Account for 1px spacing between characters
+
         return result;
     }