Fix default tag, caldav, and filter colors

app/src/main/java/org/tasks/data/CaldavCalendar.java

@@ -40,7 +40,7 @@ public final class CaldavCalendar implements Parcelable {
   private String name = "";
 
   @ColumnInfo(name = "cdl_color")
-  private int color = -1;
+  private int color;
 
   @ColumnInfo(name = "cdl_ctag")
   private String ctag;

app/src/main/java/org/tasks/data/Filter.java

@@ -28,7 +28,7 @@ public class Filter {
   private String criterion;
 
   @ColumnInfo(name = "f_color")
-  private Integer color = -1;
+  private Integer color = 0;
 
   @ColumnInfo(name = "f_icon")
   private Integer icon = -1;
@@ -79,7 +79,7 @@ public class Filter {
   }
 
   public Integer getColor() {
-    return color == null ? -1 : color;
+    return color == null ? 0 : color;
   }
 
   public void setColor(Integer color) {

app/src/main/java/org/tasks/data/TagData.java

@@ -38,7 +38,7 @@ public final class TagData implements Parcelable {
   private String name = "";
 
   @ColumnInfo(name = "color")
-  private Integer color = -1;
+  private Integer color = 0;
 
   @ColumnInfo(name = "tagOrdering")
   private String tagOrdering = "[]";
@@ -105,7 +105,7 @@ public final class TagData implements Parcelable {
   }
 
   public Integer getColor() {
-    return color;
+    return color == null ? 0 : color;
   }
 
   public void setColor(Integer color) {