Fix #956: Incorrectly handled backslash-escaped space characters within number formats (#957)

Backslash-escaped space characted sometimes not converted to quoted strings, so formatted string contains extra slashes.

CHANGELOG.md

@@ -27,6 +27,7 @@ and this project adheres to [Semantic Versioning](https://semver.org).
 
 - Fix handling for escaped enclosures and new lines in CSV Separator Inference
 - Fix MATCH an error was appearing when comparing strings against 0 (always true)
+- Fix incorrectly handled backslash-escaped space characters in number format
 - Fix wrong calculation of highest column with specified row [#700](https://github.com/PHPOffice/PhpSpreadsheet/issues/700)
 - Fix VLOOKUP 
 - Fix return type hint

src/PhpSpreadsheet/Style/NumberFormat.php

@@ -614,7 +614,7 @@ class NumberFormat extends Supervisor
         }
 
         // Convert any other escaped characters to quoted strings, e.g. (\T to "T")
-        $format = preg_replace('/(\\\([^ ]))(?=(?:[^"]|"[^"]*")*$)/u', '"${2}"', $format);
+        $format = preg_replace('/(\\\(((.)(?!((AM\/PM)|(A\/P))))|([^ ])))(?=(?:[^"]|"[^"]*")*$)/u', '"${2}"', $format);
 
         // Get the sections, there can be up to four sections, separated with a semi-colon (but only if not a quoted literal)
         $sections = preg_split('/(;)(?=(?:[^"]|"[^"]*")*$)/u', $format);

tests/data/Style/NumberFormat.php

@@ -88,6 +88,11 @@ return [
         12345.678900000001,
         '$ #,##0.000',
     ],
+    [
+        '12,345.679 €',
+        12345.678900000001,
+        '#,##0.000\ [$€-1]',
+    ],
     [
         '5.68',
         5.6788999999999996,