Improved the initial selection of spindle.

Grbl_Esp32/src/Grbl.cpp

@@ -111,6 +111,8 @@ void grbl_init() {
         for (auto s : config->_spindles) {
             s->init();
         }
+        Spindles::Spindle::switchSpindle(0, config->_spindles, spindle);
+
         config->_coolant->init();
         limits_init();
         config->_probe->init();

Grbl_Esp32/src/MachineConfig.cpp

@@ -476,11 +476,9 @@ void MachineConfig::afterParse() {
     }
 
     if (_spindles.size() == 0) {
-        log_info("Using null spindle");
+        log_info("Spindle config missing; using null spindle");
         _spindles.push_back(new Spindles::Null());
     }
-    spindle = _spindles[0];
-
     uint32_t next_tool = 100;
     for (auto s : _spindles) {
         if (s->_tool == -1) {

Grbl_Esp32/src/Spindles/Spindle.cpp

@@ -39,11 +39,17 @@ namespace Spindles {
         }
         if (candidate) {
             if (candidate != spindle) {
-                spindle->stop();
+                if (spindle != nullptr) {
+                    spindle->stop();
+                }
                 spindle = candidate;
             }
         } else {
-            if (!spindle) {
+            if (spindle == nullptr) {
+                if (spindles.size() == 0) {
+                    log_error("No spindles are defined");
+                    return;
+                }
                 spindle = spindles[0];
             }
         }