Check values when emitting ansi sequences for cursor movement, fixes #172

Author: gnodet

src/main/java/org/fusesource/jansi/Ansi.java

@@ -523,39 +523,39 @@ public Ansi cursor(final int row, final int column) {
     }
 
     public Ansi cursorToColumn(final int x) {
-        return appendEscapeSequence('G', x);
+        return x >= 0 ? appendEscapeSequence('G', x) : this;
     }
 
     public Ansi cursorUp(final int y) {
         return appendEscapeSequence('A', y);
     }
 
     public Ansi cursorDown(final int y) {
-        return appendEscapeSequence('B', y);
+        return y > 0 ? appendEscapeSequence('B', y) : this;
     }
 
     public Ansi cursorRight(final int x) {
-        return appendEscapeSequence('C', x);
+        return x > 0 ? appendEscapeSequence('C', x) : this;
     }
 
     public Ansi cursorLeft(final int x) {
-        return appendEscapeSequence('D', x);
+        return x > 0 ? appendEscapeSequence('D', x) : this;
     }
 
     public Ansi cursorDownLine() {
         return appendEscapeSequence('E');
     }
 
     public Ansi cursorDownLine(final int n) {
-        return appendEscapeSequence('E', n);
+        return n > 0 ? appendEscapeSequence('E', n) : this;
     }
 
     public Ansi cursorUpLine() {
         return appendEscapeSequence('F');
     }
 
     public Ansi cursorUpLine(final int n) {
-        return appendEscapeSequence('F', n);
+        return n > 0 ? appendEscapeSequence('F', n) : this;
     }
 
     public Ansi eraseScreen() {
@@ -575,11 +575,11 @@ public Ansi eraseLine(final Erase kind) {
     }
 
     public Ansi scrollUp(final int rows) {
-        return appendEscapeSequence('S', rows);
+        return rows > 0 ? appendEscapeSequence('S', rows) : this;
     }
 
     public Ansi scrollDown(final int rows) {
-        return appendEscapeSequence('T', rows);
+        return rows > 0 ? appendEscapeSequence('T', rows) : this;
     }
 
     public Ansi saveCursorPosition() {