patch 8.2.4860: MS-Windows: always uses current directory for executables

Problem:    MS-Windows: always uses current directory for executables.
Solution:   Check the NoDefaultCurrentDirectoryInExePath environment variable.
            (Yasuhiro Matsumoto, closes #10341)
diff --git a/src/os_win32.c b/src/os_win32.c
index 53107d5..97595d6 100644
--- a/src/os_win32.c
+++ b/src/os_win32.c
@@ -2237,7 +2237,11 @@
 		retval = FALSE;
 		goto theend;
 	    }
-	    STRCPY(pathbuf, ".;");
+
+	    if (mch_getenv("NoDefaultCurrentDirectoryInExePath") == NULL)
+		STRCPY(pathbuf, ".;");
+	    else
+		*pathbuf = NUL;
 	    STRCAT(pathbuf, p);
 	}
     }