Fix newline separators between invalid end instructions (#1640)

This commit fixes a bug from a prior refactoring where when there were
too many `end` instructions in a function, which is invalid, then
printing would confusingly "fuse" instructions together by not printing
a separator.

Author: alexcrichton

crates/wasmprinter/src/operator.rs

@@ -71,8 +71,8 @@ impl<'printer, 'state, 'a, 'b> PrintOperator<'printer, 'state, 'a, 'b> {
     fn block_end(&mut self) -> Result<()> {
         if self.printer.nesting > self.nesting_start {
             self.printer.nesting -= 1;
-            self.separator()?;
         }
+        self.separator()?;
         Ok(())
     }
 

tests/cli/print-no-panic-double-end.wat.stdout

@@ -1,4 +1,6 @@
 (module
   (type (;0;) (func))
-  (func (;0;) (type 0)end)
+  (func (;0;) (type 0)
+    end
+  )
 )

tests/cli/print-with-too-many-ends.wat

@@ -0,0 +1,5 @@
+;; RUN: print %
+
+(module
+  (func end i32.const 0 drop end)
+)

tests/cli/print-with-too-many-ends.wat.stdout

@@ -0,0 +1,9 @@
+(module
+  (type (;0;) (func))
+  (func (;0;) (type 0)
+    end
+    i32.const 0
+    drop
+    end
+  )
+)