programs/regedit: Allow importing strings with escaped NULL

[Bruno Jesus]

Simplified a bit of the logic in the process. Manually tested with reg
file from bug 27497 and other files to ensure compatibility.

Fixes https://bugs.winehq.org/show_bug.cgi?id=27497
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diff --git a/programs/regedit/regproc.c b/programs/regedit/regproc.c
index d07fdc7..9d96287 100644
--- a/programs/regedit/regproc.c
+++ b/programs/regedit/regproc.c
@@ -255,7 +255,7 @@ static DWORD getDataType(LPWSTR *lpValue, DWORD* parse_type)
 /******************************************************************************
  * Replaces escape sequences with the characters.
  */
-static void REGPROC_unescape_string(WCHAR* str)
+static int REGPROC_unescape_string(WCHAR* str)
 {
     int str_idx = 0;            /* current character under analysis */
     int val_idx = 0;            /* the last character of the unescaped string */
@@ -267,6 +267,9 @@ static void REGPROC_unescape_string(WCHAR* str)
             case 'n':
                 str[val_idx] = '\n';
                 break;
+            case '0':
+                str[val_idx] = '\0';
+                break;
             case '\\':
             case '"':
                 str[val_idx] = str[str_idx];
@@ -282,6 +285,7 @@ static void REGPROC_unescape_string(WCHAR* str)
         }
     }
     str[val_idx] = '\0';
+    return val_idx;
 }
 
 static BOOL parseKeyName(LPWSTR lpKeyName, HKEY *hKey, LPWSTR *lpKeyPath)
@@ -364,19 +368,10 @@ static LONG setValue(WCHAR* val_name, WCHAR* val_data, BOOL is_unicode)
 
     if (dwParseType == REG_SZ)          /* no conversion for string */
     {
-        REGPROC_unescape_string(val_data);
-        /* Compute dwLen after REGPROC_unescape_string because it may
-         * have changed the string length and we don't want to store
-         * the extra garbage in the registry.
-         */
-        dwLen = lstrlenW(val_data);
-        if(val_data[dwLen-1] != '"')
+        dwLen = REGPROC_unescape_string(val_data);
+        if(!dwLen || val_data[dwLen-1] != '"')
             return ERROR_INVALID_DATA;
-        if (dwLen>0 && val_data[dwLen-1]=='"')
-        {
-            dwLen--;
-            val_data[dwLen]='\0';
-        }
+        val_data[dwLen-1] = '\0'; /* remove last quotes */
         lpbData = (BYTE*) val_data;
         dwLen++;  /* include terminating null */
         dwLen = dwLen * sizeof(WCHAR); /* size is in bytes */