math/saga: fix build on GCC architectures

Returning NULL as bool is not ok.
--- globe_gores.lo ---
globe_gores.cpp: In member function 'bool CGlobe_Gores::Add_Gore(int, int)':
globe_gores.cpp:210:16: error: converting to 'bool' from 'std::nullptr_t' requires direct-initialization [-fpermissive]
  210 |   return( NULL );

PR:		246720
Approved by:	rhurlin@gwdg.de (maintainer)

1 files changed, 11 insertions, 0 deletions

diff --git a/math/saga/files/patch-src_tools_projection_pj__proj4_globe__gores.cpp b/math/saga/files/patch-src_tools_projection_pj__proj4_globe__gores.cpp
new file mode 100644
index 000000000000..2b3a3a970083
--- /dev/null
+++ b/math/saga/files/patch-src_tools_projection_pj__proj4_globe__gores.cpp
@@ -0,0 +1,11 @@
+--- src/tools/projection/pj_proj4/globe_gores.cpp.orig	2020-05-24 11:21:37 UTC
++++ src/tools/projection/pj_proj4/globe_gores.cpp
+@@ -207,7 +207,7 @@ bool CGlobe_Gores::Add_Gore(int iGore, int nGores)
+ 
+ 		SG_Get_Tool_Library_Manager().Delete_Tool(pTool);
+ 
+-		return( NULL );
++		return( false );
+ 	}
+ 
+ 	CSG_Grid	*pGore	= pTool->Get_Parameter("GRID")->asGrid();