Fix a linter warning "Do not use unless with else"

Author: andrykonchin

src/main/ruby/truffleruby/core/enumerable.rb

@@ -525,33 +525,33 @@ def inject(initial=undefined, sym=undefined, &block)
       warn 'given block not used', uplevel: 1
     end
 
-    unless Primitive.undefined?(sym) && block_given?
-      # Do the sym version:
-      #   inject(symbol) -> object
-      #   inject(initial_operand, symbol) -> object
-
-      sym, initial = initial, undefined if Primitive.undefined?(sym)
-      sym = sym.to_sym
+    if Primitive.undefined?(sym) && block_given?
+      # Do the block version:
+      #   inject {|memo, operand| ... } -> object
+      #   inject(initial_operand) {|memo, operand| ... } -> object
 
       each do
         o = Primitive.single_block_arg
         if Primitive.undefined? initial
           initial = o
         else
-          initial = initial.__send__(sym, o)
+          initial = yield(initial, o)
         end
       end
-
-      # Do the block version:
-      #   inject {|memo, operand| ... } -> object
-      #   inject(initial_operand) {|memo, operand| ... } -> object
     else
+      # Do the sym version:
+      #   inject(symbol) -> object
+      #   inject(initial_operand, symbol) -> object
+
+      sym, initial = initial, undefined if Primitive.undefined?(sym)
+      sym = sym.to_sym
+
       each do
         o = Primitive.single_block_arg
         if Primitive.undefined? initial
           initial = o
         else
-          initial = yield(initial, o)
+          initial = initial.__send__(sym, o)
         end
       end
     end