Bug#50337 --defaults-file=~/something doesn't work anymore

Before this fix, opening a configuration file located under "~" failed.
To evaluate the "~" path, home_dir needs to be initialized.
The 'home_dir' variable was initialized too late in my_init().

This fix:
- moved the home_dir initialization from my_init() to my_basic_init(),
  using getenv("HOME"))
- moved the initialization of my_umask / my_umask_dir also to
  my_basic_init(), to have all the my_umask / my_umask_dir init code in the
  same place.

The second part is not strictly required, but makes the code more
maintainable.

Tested the fix manually.

No MTR tests added, because MTR should not access or modify the $HOME
directory of the user running tests.

mysys/my_init.c

@@ -74,6 +74,8 @@ static MYSQL_FILE instrumented_stdin;
 */
 my_bool my_basic_init(void)
 {
+  char * str;
+
   if (my_basic_init_done)
     return 0;
   my_basic_init_done= 1;
@@ -82,6 +84,19 @@ my_bool my_basic_init(void)
   my_umask= 0660;                       /* Default umask for new files */
   my_umask_dir= 0700;                   /* Default umask for new directories */
 
+#ifndef VMS
+  /* Default creation of new files */
+  if ((str= getenv("UMASK")) != 0)
+    my_umask= (int) (atoi_octal(str) | 0600);
+  /* Default creation of new dir's */
+  if ((str= getenv("UMASK_DIR")) != 0)
+    my_umask_dir= (int) (atoi_octal(str) | 0700);
+#endif
+
+  /* $HOME is needed early to parse configuration files located in ~/ */
+  if ((home_dir= getenv("HOME")) != 0)
+    home_dir= intern_filename(home_dir_buff, home_dir);
+
   init_glob_errs();
 
   instrumented_stdin.m_file= stdin;
@@ -124,7 +139,6 @@ my_bool my_basic_init(void)
 
 my_bool my_init(void)
 {
-  char * str;
   if (my_init_done)
     return 0;
   my_init_done= 1;
@@ -142,24 +156,11 @@ my_bool my_init(void)
   {
     DBUG_ENTER("my_init");
     DBUG_PROCESS((char*) (my_progname ? my_progname : "unknown"));
-    if (!home_dir)
-    {					/* Don't initialize twice */
     my_win_init();
-      if ((home_dir=getenv("HOME")) != 0)
-	home_dir=intern_filename(home_dir_buff,home_dir);
-#ifndef VMS
-      /* Default creation of new files */
-      if ((str=getenv("UMASK")) != 0)
-	my_umask=(int) (atoi_octal(str) | 0600);
-	/* Default creation of new dir's */
-      if ((str=getenv("UMASK_DIR")) != 0)
-	my_umask_dir=(int) (atoi_octal(str) | 0700);
-#endif
 #ifdef VMS
     init_ctype();                       /* Stupid linker don't link _ctype.c */
 #endif
-      DBUG_PRINT("exit",("home: '%s'",home_dir));
-    }
+    DBUG_PRINT("exit", ("home: '%s'", home_dir));
 #ifdef __WIN__
     win32_init_tcp_ip();
 #endif