fix(detect_chip): Select correct loader before further operations to avoid silent failures

If there is a return statement in finally block, it will prevent
unhandled exceptions from try block and all exceptions from except
block to be propagated.

Also, checking if esptool communicates with stub is performed earlier.

Closes espressif#1025

Author: Honza0297

esptool/cmds.py

@@ -97,6 +97,14 @@ def detect_chip(
     if detect_port.serial_port.startswith("rfc2217:"):
         detect_port.USES_RFC2217 = True
     detect_port.connect(connect_mode, connect_attempts, detecting=True)
+
+    def check_if_stub(instance):
+        print(f" {instance.CHIP_NAME}", end="")
+        if detect_port.sync_stub_detected:
+            instance = instance.STUB_CLASS(instance)
+            instance.sync_stub_detected = True
+        return instance
+
     try:
         print("Detecting chip type...", end="")
         chip_id = detect_port.get_chip_id()
@@ -112,6 +120,7 @@ def detect_chip(
                     )  # Dummy read to check Secure Download mode
                 except UnsupportedCommandError:
                     inst.secure_download_mode = True
+                inst = check_if_stub(inst)
                 inst._post_connect()
                 break
         else:
@@ -137,6 +146,7 @@ def detect_chip(
             for cls in ROM_LIST:
                 if chip_magic_value in cls.CHIP_DETECT_MAGIC_VALUE:
                     inst = cls(detect_port._port, baud, trace_enabled=trace_enabled)
+                    inst = check_if_stub(inst)
                     inst._post_connect()
                     inst.check_chip_id()
                     break
@@ -148,14 +158,9 @@ def detect_chip(
                 "Probably this means Secure Download Mode is enabled, "
                 "autodetection will not work. Need to manually specify the chip."
             )
-    finally:
-        if inst is not None:
-            print(" %s" % inst.CHIP_NAME, end="")
-            if detect_port.sync_stub_detected:
-                inst = inst.STUB_CLASS(inst)
-                inst.sync_stub_detected = True
-            print("")  # end line
-            return inst
+    if inst is not None:
+        return inst
+
     raise FatalError(
         f"{err_msg} Failed to autodetect chip type."
         "\nProbably it is unsupported by this version of esptool."