Fix wallet backwards paid flag melt (#659)

* backwards compat for melt quote without state

* backwards compat for quote without state

cashu/core/base.py

@@ -331,6 +331,13 @@ def from_row(cls, row: Row):
     def from_resp_wallet(
         cls, melt_quote_resp, mint: str, amount: int, unit: str, request: str
     ):
+        # BEGIN: BACKWARDS COMPATIBILITY < 0.16.0: "paid" field to "state"
+        if melt_quote_resp.state is None:
+            if melt_quote_resp.paid is True:
+                melt_quote_resp.state = MeltQuoteState.paid
+            elif melt_quote_resp.paid is False:
+                melt_quote_resp.state = MeltQuoteState.unpaid
+        # END: BACKWARDS COMPATIBILITY < 0.16.0
         return cls(
             quote=melt_quote_resp.quote,
             method="bolt11",
@@ -433,6 +440,13 @@ def from_row(cls, row: Row):
 
     @classmethod
     def from_resp_wallet(cls, mint_quote_resp, mint: str, amount: int, unit: str):
+        # BEGIN: BACKWARDS COMPATIBILITY < 0.16.0: "paid" field to "state"
+        if mint_quote_resp.state is None:
+            if mint_quote_resp.paid is True:
+                mint_quote_resp.state = MintQuoteState.paid
+            elif mint_quote_resp.paid is False:
+                mint_quote_resp.state = MintQuoteState.unpaid
+        # END: BACKWARDS COMPATIBILITY < 0.16.0
         return cls(
             quote=mint_quote_resp.quote,
             method="bolt11",