internal/ethapi: fix panic in debug methods (ethereum#31157)

Fixes an error when the block is not found in debug methods.

Author: s1na

internal/ethapi/api.go

@@ -1992,7 +1992,7 @@ func (api *DebugAPI) GetRawHeader(ctx context.Context, blockNrOrHash rpc.BlockNu
 		hash = h
 	} else {
 		block, err := api.b.BlockByNumberOrHash(ctx, blockNrOrHash)
-		if err != nil {
+		if block == nil || err != nil {
 			return nil, err
 		}
 		hash = block.Hash()
@@ -2011,7 +2011,7 @@ func (api *DebugAPI) GetRawBlock(ctx context.Context, blockNrOrHash rpc.BlockNum
 		hash = h
 	} else {
 		block, err := api.b.BlockByNumberOrHash(ctx, blockNrOrHash)
-		if err != nil {
+		if block == nil || err != nil {
 			return nil, err
 		}
 		hash = block.Hash()
@@ -2030,7 +2030,7 @@ func (api *DebugAPI) GetRawReceipts(ctx context.Context, blockNrOrHash rpc.Block
 		hash = h
 	} else {
 		block, err := api.b.BlockByNumberOrHash(ctx, blockNrOrHash)
-		if err != nil {
+		if block == nil || err != nil {
 			return nil, err
 		}
 		hash = block.Hash()