Fix decompressing using qstrs after running the VM

The qstr state still pointed to qstr pools in the released MP heap.

Author: tannewt

main.c

@@ -219,6 +219,10 @@ STATIC void stop_mp(void) {
     usb_background();
     #endif
 
+    // Set the qstr pool back to the const pools. The heap allocated ones will
+    // be overwritten.
+    qstr_reset();
+
     gc_deinit();
 }
 

py/qstr.c

@@ -122,9 +122,13 @@ extern const qstr_pool_t MICROPY_QSTR_EXTRA_POOL;
 #define CONST_POOL mp_qstr_const_pool
 #endif
 
-void qstr_init(void) {
+void qstr_reset(void) {
     MP_STATE_VM(last_pool) = (qstr_pool_t *)&CONST_POOL; // we won't modify the const_pool since it has no allocated room left
     MP_STATE_VM(qstr_last_chunk) = NULL;
+}
+
+void qstr_init(void) {
+    qstr_reset();
 
     #if MICROPY_PY_THREAD && !MICROPY_PY_THREAD_GIL
     mp_thread_mutex_init(&MP_STATE_VM(qstr_mutex));

py/qstr.h

@@ -78,6 +78,7 @@ typedef struct _qstr_pool_t {
 
 #define QSTR_TOTAL() (MP_STATE_VM(last_pool)->total_prev_len + MP_STATE_VM(last_pool)->len)
 
+void qstr_reset(void);
 void qstr_init(void);
 
 mp_uint_t qstr_compute_hash(const byte *data, size_t len);