Don't try to fixup invalid e.p. square if the position is invalid

En passant fixup requires generating a list of legal moves, which can
fail with an array index out of bounds exception if there is a pawn on
the first/last rank.

DroidFishApp/src/main/java/org/petero/droidfish/activities/EditBoard.java

@@ -442,6 +442,7 @@ public class EditBoard extends Activity {
 
     private void setPosFields() {
         setEPFile(getEPFile()); // To handle sideToMove change
+        if (isValid())
             TextIO.fixupEPSquare(cb.pos);
         TextIO.removeBogusCastleFlags(cb.pos);
     }
@@ -478,6 +479,16 @@ public class EditBoard extends Activity {
         return false;
     }
 
+    /** Return true if the position is valid. */
+    private boolean isValid() {
+        try {
+            TextIO.readFEN(TextIO.toFEN(cb.pos));
+            return true;
+        } catch (ChessParseError e) {
+            return false;
+        }
+    }
+
     private String getParseErrString(ChessParseError e) {
         if (e.resourceId == -1)
             return e.getMessage();