Cleaned Code & Fixed Some Errors

MathPad/MPPowerTerm.m

@@ -13,14 +13,9 @@
 
 - (NSDecimalNumber *)doEvaluation:(NSError *__autoreleasing *)error
 {
-    NSDecimalNumber *exponent = [[self expressionAtIndex:0] evaluate:error];
-    if (!exponent) {
-        return nil;
-    }
+    MPEvaluateExpression(exponent, 0);
     NSDecimalNumber *base = [self.baseTerm evaluate:error];
-    if (!base) {
-        return nil;
-    }
+    ReturnNilIfNil(base);
     if ([base isEqualToNumber:@(0)] && [exponent isEqualToNumber:@(0)]) {
         // The C pow function returns 1 for pow(0, 0). Mathematically this should be undefined.
         if (error) {