feature #3746 [Validator] Disallow empty file in FileValidator (megazoll)

This PR was merged into the master branch.

Discussion
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[Validator] Disallow empty file in FileValidator

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes (symfony/symfony#11125)
| Applies to    | 2.6+

Commits
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80673d5 Disallow empty file in FileValidator

Author: weaverryan

reference/constraints/File.rst

@@ -23,6 +23,7 @@ form type.
 |                | - `mimeTypes`_                                                      |
 |                | - `maxSizeMessage`_                                                 |
 |                | - `mimeTypesMessage`_                                               |
+|                | - `disallowEmptyMessage`_                                           |
 |                | - `notFoundMessage`_                                                |
 |                | - `notReadableMessage`_                                             |
 |                | - `uploadIniSizeErrorMessage`_                                      |
@@ -194,6 +195,18 @@ mimeTypesMessage
 The message displayed if the mime type of the file is not a valid mime type
 per the `mimeTypes`_ option.
 
+disallowEmptyMessage
+~~~~~~~~~~~~~~~~~~~~
+
+.. versionadded:: 2.6
+    The ``disallowEmptyMessage`` option was introduced in Symfony 2.6. Prior to 2.6,
+    if the user uploaded an empty file, no validation error occurred.
+
+**type**: ``string`` **default**: ``An empty file is not allowed.``
+
+This constraint checks if the uploaded file is empty (i.e. 0 bytes). If it is,
+this message is displayed.
+
 notFoundMessage
 ~~~~~~~~~~~~~~~