Fixed segfault which occured when open ing the module editor, loading a...

Fixed segfault which occured when open ing the module editor, loading a module, closing it, and opening the module editor again. This was 
caused by prematurely deleting the module editor's m_Pcb pointer, which has the same value (points to the same structure) as 
g_ModuleEditor_Pcb hence should not be 
deleted. 

include/wxstruct.h

@@ -21,7 +21,7 @@
 #include <vector>
 
 #ifndef SAFE_DELETE
-#define SAFE_DELETE(p) delete (p); (p) = NULL; 
+#define SAFE_DELETE(p) delete (p); (p) = NULL; //C++ guarantees that operator delete checks its argument for null-ness
 #endif
 
 #define INTERNAL_UNIT_TYPE      0        // Internal unit = inch

pcbnew/basepcbframe.cpp

@@ -68,6 +68,7 @@ WinEDA_BasePcbFrame::~WinEDA_BasePcbFrame( void )
 
 void WinEDA_BasePcbFrame::SetBOARD( BOARD* aBoard )
 {
+    if(m_Pcb != g_ModuleEditor_Pcb) 
 		delete m_Pcb;
     m_Pcb = aBoard;
 }

pcbnew/locate.cpp

@@ -382,7 +382,7 @@ TRACK* Locate_Piste_Connectee( TRACK* PtRefSegm, TRACK* pt_base,
             if( PtSegmN == PtRefSegm )
                 goto suite;
 
-            /* max_dist is the max distance between 2 tack ends which ensure a copper continuty */
+            /* max_dist is the max distance between 2 track ends which ensure a copper continuty */
             max_dist = (PtSegmN->m_Width + PtRefSegm->m_Width)/2;
 
             if( IsPointsAreNear(pos_ref, PtSegmN->m_Start, max_dist) )

pcbnew/moduleframe.cpp

@@ -136,7 +136,7 @@ WinEDA_ModuleEditFrame::WinEDA_ModuleEditFrame( wxWindow* father, WinEDA_App* pa
 
     m_Pcb->m_PcbFrame = this;
     m_CurrentScreen   = ScreenModule;
-    SetCurItem( NULL );
+	m_CurrentScreen->SetCurItem( NULL ); 
     GetSettings();
 
     wxSize GridSize( 500, 500 );

pcbnew/pcbframe.cpp

@@ -250,7 +250,7 @@ WinEDA_PcbFrame::~WinEDA_PcbFrame()
     m_Parent->m_PcbFrame = NULL;
     m_CurrentScreen = ScreenPcb;
     delete m_drc;
-    delete m_Pcb;
+    if(m_Pcb != g_ModuleEditor_Pcb) delete m_Pcb;
 }