kernelbase: Don't strip leading dots in relative paths.

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=49315
Signed-off-by: Rémi Bernon <rbernon@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>
(cherry picked from commit c27b246)

dlls/kernelbase/path.c

@@ -1389,7 +1389,7 @@ BOOL WINAPI PathCanonicalizeW(WCHAR *buffer, const WCHAR *path)
             {
                 src += 2; /* Skip .\ */
             }
-            else if (src[1] == '.' && (dst == buffer || dst[-1] == '\\'))
+            else if (src[1] == '.' && dst != buffer && dst[-1] == '\\')
             {
                 /* \.. backs up a directory, over the root if it has no \ following X:.
                  * .. is ignored if it would remove a UNC server name or initial \\

dlls/shlwapi/tests/path.c

@@ -714,6 +714,15 @@ static void test_PathCombineA(void)
     ok(!lstrcmpA(str, "C:\\"), "Expected C:\\, got %s\n", str);
     ok(GetLastError() == 0xdeadbeef, "Expected 0xdeadbeef, got %d\n", GetLastError());
 
+    /* try relative paths */
+    /* try forward slashes */
+    SetLastError(0xdeadbeef);
+    lstrcpyA(dest, "control");
+    str = PathCombineA(dest, "../../../one/two/", "*");
+    ok(str == dest, "Expected str == dest, got %p\n", str);
+    ok(!lstrcmpA(str, "../../../one/two/\\*"), "Expected ../../../one/two/\\*, got %s\n", str);
+    ok(GetLastError() == 0xdeadbeef, "Expected 0xdeadbeef, got %d\n", GetLastError());
+
     memset(too_long, 'a', LONG_LEN);
     too_long[LONG_LEN - 1] = '\0';
 
@@ -1039,6 +1048,22 @@ static void test_PathCanonicalizeA(void)
        !lstrcmpA(dest, "C:\\one/"), /* Vista */
        "Expected \"C:\\one/.\" or \"C:\\one/\", got \"%s\"\n", dest);
 
+    /* try relative forward slashes */
+    lstrcpyA(dest, "test");
+    SetLastError(0xdeadbeef);
+    res = PathCanonicalizeA(dest, "../../one/two/");
+    ok(res, "Expected success\n");
+    ok(GetLastError() == 0xdeadbeef, "Expected 0xdeadbeef, got %d\n", GetLastError());
+    ok(!lstrcmpA(dest, "../../one/two/"), "Expected ../../one/two/, got %s\n", dest);
+
+    /* try relative forward slashes */
+    lstrcpyA(dest, "test");
+    SetLastError(0xdeadbeef);
+    res = PathCanonicalizeA(dest, "../../one/two/\\*");
+    ok(res, "Expected success\n");
+    ok(GetLastError() == 0xdeadbeef, "Expected 0xdeadbeef, got %d\n", GetLastError());
+    ok(!lstrcmpA(dest, "../../one/two/\\*"), "Expected ../../one/two/\\*, got %s\n", dest);
+
     /* try forward slashes with change dirs
      * NOTE: if there is a forward slash in between two backslashes,
      * everything in between the two backslashes is considered on dir