document that nEndPos of -1 is all text

Change-Id: I4646e1ef09db3a637248cff53cbbafb214219cf8
Reviewed-on: https://gerrit.libreoffice.org/59542
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

include/vcl/weld.hxx

@@ -484,6 +484,7 @@ public:
     virtual OUString get_text() const = 0;
     virtual void set_width_chars(int nChars) = 0;
     virtual void set_max_length(int nChars) = 0;
+    // nEndPos can be -1 in order to select all text
     virtual void select_region(int nStartPos, int nEndPos) = 0;
     virtual bool get_selection_bounds(int& rStartPos, int& rEndPos) = 0;
     virtual void set_position(int nCursorPos) = 0;

sw/source/ui/fldui/inpdlg.cxx

@@ -106,7 +106,7 @@ SwFieldInputDlg::SwFieldInputDlg(weld::Window *pParent, SwWrtShell &rS,
 
     // preselect all text to allow quickly changing the content
     if (bEnable)
-        m_xEditED->select_region(0, m_xEditED->get_text().getLength());
+        m_xEditED->select_region(0, -1);
 }
 
 SwFieldInputDlg::~SwFieldInputDlg()