Fix escaping of ebook-convert options

lib/utils/command.js

@@ -1,3 +1,4 @@
+var is = require('is');
 var childProcess = require('child_process');
 var spawn = require('spawn-cmd').spawn;
 var Promise = require('./promise');
@@ -54,12 +55,29 @@ function spawnCmd(command, args, options) {
     return d.promise;
 }
 
-// Transform an option object to a command line string
-function escapeShellArg(s) {
-    s = s.replace(/"/g, '\\"');
-    return '"' + s + '"';
+/**
+    Transform an option object to a command line string
+
+    @param {String|number} value
+    @param {String}
+*/
+function escapeShellArg(value) {
+    if (is.number(value)) {
+        return value;
+    }
+
+    value = String(value);
+    value = value.replace(/"/g, '\\"');
+
+    return '"' + value + '"';
 }
 
+/**
+    Transform a map of options into a command line arguments string
+
+    @param {Object} options
+    @return {String}
+*/
 function optionsToShellArgs(options) {
     var result = [];
 
@@ -69,11 +87,12 @@ function optionsToShellArgs(options) {
         if (value === null || value === undefined || value === false) {
             continue;
         }
-        if (value === true) {
-            result.push(key);
-        }
 
-        result.push(key + '=' + escapeShellArg(value));
+        if (is.bool(value)) {
+            result.push(key);
+        } else {
+            result.push(key + '=' + escapeShellArg(value));
+        }
     }
 
     return result.join(' ');