PDF plotter: fix a rare pen width issue when plotting many pages in one file.

Fixes https://gitlab.com/kicad/code/kicad/-/issues/20805

(cherry picked from commit a02f1f2411)

common/plotters/PDF_plotter.cpp

@@ -678,6 +678,10 @@ void PDF_PLOTTER::StartPage( const wxString& aPageNumber, const wxString& aPageN
     m_paperSize.x *= 10.0 / m_iuPerDeviceUnit;
     m_paperSize.y *= 10.0 / m_iuPerDeviceUnit;
 
+    // Set m_currentPenWidth to a unused value to ensure the pen width
+    // will be initialized to a the right value in pdf file by the first item to plot
+    m_currentPenWidth = 0;
+
     // Open the content stream; the page object will go later
     m_pageStreamHandle = startPdfStream();