FEM: gmsh tools, fix regression and explizit use double quotes in geo file

Author: berndhahnebach

src/Mod/Fem/femmesh/gmshtools.py

@@ -561,7 +561,8 @@ def write_geo(self):
         geo.write("// geo file for meshing with Gmsh meshing software created by FreeCAD\n")
         geo.write("\n")
         geo.write("// open brep geometry\n")
-        geo.write("Merge "" + self.temp_file_geometry + "";\n")
+        # explizit use double quotes in geo file
+        geo.write('Merge "{}";\n'.format(self.temp_file_geometry))
         geo.write("\n")
         if self.group_elements:
             # print("  We are going to have to find elements to make mesh groups for.")
@@ -708,7 +709,8 @@ def write_geo(self):
                 "for one material there is no group defined;\n")
         geo.write("// Ignore Physical definitions and save all elements;\n")
         geo.write("Mesh.SaveAll = 1;\n")
-        geo.write('Save "' + self.temp_file_mesh + '";\n')
+        # explizit use double quotes in geo file
+        geo.write('Save "{}";\n'.format(self.temp_file_mesh))
         geo.write("\n\n")
         geo.write("//////////////////////////////////////////////////////////////////////\n")
         geo.write("// Gmsh documentation:\n")