Misc. fixes to compiler warnings, etc.

Marlin/src/gcode/bedlevel/abl/G29.cpp

 
       bool zig = PR_OUTER_END & 1;  // Always end at RIGHT and BACK_PROBE_BED_POSITION
 
+      measured_z = 0;
+
       // Outer loop is Y with PROBE_Y_FIRST disabled
       for (uint8_t PR_OUTER_VAR = 0; PR_OUTER_VAR < PR_OUTER_END && !isnan(measured_z); PR_OUTER_VAR++) {
 

Marlin/src/gcode/motion/G2_G3.cpp

   #if ENABLED(CNC_WORKSPACE_PLANES)
     AxisEnum p_axis, q_axis, l_axis;
     switch (gcode.workspace_plane) {
+      default:
       case GcodeSuite::PLANE_XY: p_axis = X_AXIS; q_axis = Y_AXIS; l_axis = Z_AXIS; break;
       case GcodeSuite::PLANE_ZX: p_axis = Z_AXIS; q_axis = X_AXIS; l_axis = Y_AXIS; break;
       case GcodeSuite::PLANE_YZ: p_axis = Y_AXIS; q_axis = Z_AXIS; l_axis = X_AXIS; break;

Marlin/src/module/configuration_store.cpp

  *  195  M206 XYZ  home_offset                      (float x3)
  *  207  M218 XYZ  hotend_offset                    (float x3 per additional hotend)
  *
- * Global Leveling:
+ * Global Leveling:                                 4 bytes
  *  219            z_fade_height                    (float)
  *
  * MESH_BED_LEVELING:                               43 bytes
  * ABL_PLANAR:                                      36 bytes
  *  270            planner.bed_level_matrix         (matrix_3x3 = float x9)
  *
- * AUTO_BED_LEVELING_BILINEAR:                      47 bytes
+ * AUTO_BED_LEVELING_BILINEAR:                      46 bytes
  *  306            GRID_MAX_POINTS_X                (uint8_t)
  *  307            GRID_MAX_POINTS_Y                (uint8_t)
  *  308            bilinear_grid_spacing            (int x2)