fix reduce() TypeError in hyperopts

docs/hyperopt.md

@@ -122,6 +122,7 @@ So let's write the buy strategy using these values:
                         dataframe['macd'], dataframe['macdsignal']
                     ))
 
+            if conditions:
                 dataframe.loc[
                     reduce(lambda x, y: x & y, conditions),
                     'buy'] = 1

freqtrade/optimize/default_hyperopt.py

@@ -70,6 +70,7 @@ class DefaultHyperOpts(IHyperOpt):
                         dataframe['close'], dataframe['sar']
                     ))
 
+            if conditions:
                 dataframe.loc[
                     reduce(lambda x, y: x & y, conditions),
                     'buy'] = 1
@@ -129,6 +130,7 @@ class DefaultHyperOpts(IHyperOpt):
                         dataframe['sar'], dataframe['close']
                     ))
 
+            if conditions:
                 dataframe.loc[
                     reduce(lambda x, y: x & y, conditions),
                     'sell'] = 1

user_data/hyperopts/sample_hyperopt.py

@@ -79,6 +79,7 @@ class SampleHyperOpts(IHyperOpt):
                         dataframe['close'], dataframe['sar']
                     ))
 
+            if conditions:
                 dataframe.loc[
                     reduce(lambda x, y: x & y, conditions),
                     'buy'] = 1
@@ -138,6 +139,7 @@ class SampleHyperOpts(IHyperOpt):
                         dataframe['sar'], dataframe['close']
                     ))
 
+            if conditions:
                 dataframe.loc[
                     reduce(lambda x, y: x & y, conditions),
                     'sell'] = 1