Fix some compilation warnings

[txgk]

When I compile the library with warnings enabled, I get some unpleasant output during the build stage:

Source/geom.c: In function ‘tesedgeIntersect’:
Source/geom.c:220:50: warning: suggest braces around empty body in an ‘else’ statement [-Wempty-body]
  220 |         if( ! VertLeq( o1, d1 )) { Swap( o1, d1 ); }
      |                                                  ^
Source/geom.c:221:50: warning: suggest braces around empty body in an ‘else’ statement [-Wempty-body]
  221 |         if( ! VertLeq( o2, d2 )) { Swap( o2, d2 ); }
      |                                                  ^
Source/geom.c:222:50: warning: suggest braces around empty body in an ‘else’ statement [-Wempty-body]
  222 |         if( ! VertLeq( o1, o2 )) { Swap( o1, o2 ); Swap( d1, d2 ); }
      |                                                  ^
Source/geom.c:222:66: warning: suggest braces around empty body in an ‘else’ statement [-Wempty-body]
  222 |         if( ! VertLeq( o1, o2 )) { Swap( o1, o2 ); Swap( d1, d2 ); }
      |                                                                  ^
Source/geom.c:243:51: warning: suggest braces around empty body in an ‘else’ statement [-Wempty-body]
  243 |         if( ! TransLeq( o1, d1 )) { Swap( o1, d1 ); }
      |                                                   ^
Source/geom.c:244:51: warning: suggest braces around empty body in an ‘else’ statement [-Wempty-body]
  244 |         if( ! TransLeq( o2, d2 )) { Swap( o2, d2 ); }
      |                                                   ^
Source/geom.c:245:51: warning: suggest braces around empty body in an ‘else’ statement [-Wempty-body]
  245 |         if( ! TransLeq( o1, o2 )) { Swap( o1, o2 ); Swap( d1, d2 ); }
      |                                                   ^
Source/geom.c:245:67: warning: suggest braces around empty body in an ‘else’ statement [-Wempty-body]
  245 |         if( ! TransLeq( o1, o2 )) { Swap( o1, o2 ); Swap( d1, d2 ); }
      |                                                                   ^
Source/mesh.c: In function ‘tessMeshFlipEdge’:
Source/mesh.c:751:34: warning: unused parameter ‘mesh’ [-Wunused-parameter]
  751 | void tessMeshFlipEdge( TESSmesh *mesh, TESShalfEdge *edge )
      |                        ~~~~~~~~~~^~~~
Source/priorityq.c: In function ‘pqInit’:
Source/priorityq.c:385:45: warning: suggest braces around empty body in an ‘else’ statement [-Wempty-body]
  385 |                                 Swap( i, j );
      |                                             ^
Source/priorityq.c:387:37: warning: suggest braces around empty body in an ‘else’ statement [-Wempty-body]
  387 |                         Swap( i, j ); /* Undo last swap */
      |

I provide a little patch to fix that if you're interested, otherwise never mind ;)

[sfreilich]

Looks good, thanks!