improve emterpreter error on bad file (#5354)

Author: kripken

tools/emterpretify.py

@@ -991,7 +991,7 @@ def post_process_code(code):
 
     js += ['''
   var bytecodeFile = Module['emterpreterFile'];
-  assert(bytecodeFile instanceof ArrayBuffer, 'bad emterpreter file');
+  assert(bytecodeFile instanceof ArrayBuffer, 'bad or missing emterpreter file. if you compiled to JS (and not HTML) make sure you set Module["emterpreterFile"]');
   var codeSize = %d;
   HEAPU8.set(new Uint8Array(bytecodeFile).subarray(0, codeSize), eb);
   assert(HEAPU8[eb] === %d);
@@ -1001,7 +1001,9 @@ def post_process_code(code):
   var relocationsStart = (codeSize+3) >> 2;
   var relocations = (new Uint32Array(bytecodeFile)).subarray(relocationsStart);
   assert(relocations.length === %d);
-  if (relocations.length > 0) assert(relocations[0] === %d);
+  if (relocations.length > 0) {
+    assert(relocations[0] === %d);
+  }
 ''' % (len(all_code), all_code[0], all_code[1], all_code[2], all_code[3], len(relocations), relocations[0])]
 
   else: