Do not crash on failed speaker volume retrieval

Fixes #63.

wideq/ac.py

@@ -3,6 +3,7 @@
 import enum
 
 from .client import Device
+from .core import FailedRequestError
 
 
 class ACVSwingMode(enum.Enum):
@@ -256,8 +257,11 @@ class ACDevice(Device):
     def get_volume(self):
         """Get the speaker volume level."""
 
-        value = self._get_control('SpkVolume')
-        return int(value)
+        try:
+            value = self._get_control('SpkVolume')
+            return int(value)
+        except FailedRequestError:
+            return 0  # Device does not support volume control.
 
     def poll(self):
         """Poll the device's current state.

wideq/core.py

@@ -85,6 +85,15 @@ class TokenError(APIError):
         pass
 
 
+class FailedRequestError(APIError):
+    """A failed request typically indicates an unsupported control on a
+    device.
+    """
+
+    def __init__(self):
+        pass
+
+
 class InvalidRequestError(APIError):
     """The server rejected a request as invalid."""
 
@@ -105,6 +114,7 @@ class MonitorError(APIError):
 API_ERRORS = {
     "0102": NotLoggedInError,
     "0106": NotConnectedError,
+    "0100": FailedRequestError,
     9000: InvalidRequestError,  # Surprisingly, an integer (not a string).
 }