fix warnings for gcc 10 and clang 10

source/src/world.cpp

@@ -478,7 +478,7 @@ void deleteentity(char *ns)
     if(t == SOUND) deletesoundentity(e);
     conoutf("deleted entity #%d (%s)", n, entnames[e.type]);
     deleted_ents.add(e);
-    memset(&e, 0, sizeof(persistent_entity));
+    memset((void *)&e, 0, sizeof(persistent_entity));
     e.type = NOTUSED;
     if(t == LIGHT) calclight();
     unsavededits++;
@@ -751,7 +751,7 @@ bool empty_world(int factor, bool force)    // main empty world creation routine
         clearheaderextras();
         unsavededits = oldunsavededits;
     }
-    strncpy(hdr.head, "ACMP", 4);
+    memcpy(hdr.head, "ACMP", 4);
     hdr.version = MAPVERSION;
     hdr.headersize = sizeof(header);
     hdr.sfactor = sfactor;