parser: check that functions return in all if/else branches

vlib/math/complex/complex.v

@@ -489,8 +489,7 @@ pub fn (c Complex) acsch() Complex {
 		)
 		.divide(c)
 		.ln()
-	}
-	if(c.re > 0) {
+	} else {
 		return one.add(
 			one.add(
 				c.pow(2) 

vlib/math/fractions/fraction.v

@@ -19,6 +19,7 @@ pub fn fraction(n i64, d i64) Fraction{
 	} 
 	else {
 		panic('Denominator cannot be zero')
+		return Fraction{} // TODO remove return
 	}
 }