icu: fix NULL dereference in `enumEitherTrie`

According to the business logic and assertions `idx` and `data32`
variables cannot be equal to NULL at the same time. However, we
cannot rely on assertions.

Let's check that explicitly. If this situation occurs somehow
the function exits as we cannot recover from this situation: we
don't have sources, from which values for enumeration can be taken.
Moreover, continuing of the code execution is such situation may
lead to accessing NULL if `c<limit`.

Closes tarantool/security#59

NO_CHANGELOG=<security fix>
NO_DOC=<security fix>
NO_TEST=<third-party security fix>

static-build/cmake/AddDependencyProjects.cmake

@@ -115,6 +115,7 @@ ExternalProject_Add(icu
         cat <BINARY_DIR>/uconfig.h.prepend <INSTALL_DIR>/include/unicode/uconfig.h >> <BINARY_DIR>/uconfig.h &&
         ${CMAKE_COMMAND} -E copy_if_different <BINARY_DIR>/uconfig.h <INSTALL_DIR>/include/unicode/uconfig.h
     PATCH_COMMAND patch -d <SOURCE_DIR> -p1 -i "${PATCHES_DIR}/icu-tarantool-security-45.patch"
+    COMMAND       patch -d <SOURCE_DIR> -p1 -i "${PATCHES_DIR}/icu-tarantool-security-59.patch"
 )
 set(TARANTOOL_DEPENDS icu ${TARANTOOL_DEPENDS})
 

static-build/patches/icu-tarantool-security-59.patch

+diff --git a/source/common/utrie2.cpp b/source/common/utrie2.cpp
+index 24ef578..359952a 100644
+--- a/source/common/utrie2.cpp
++++ b/source/common/utrie2.cpp
+@@ -574,7 +574,15 @@ enumEitherTrie(const UTrie2 *trie,
+                     c+=UTRIE2_DATA_BLOCK_LENGTH;
+                 } else {
+                     for(j=0; j<UTRIE2_DATA_BLOCK_LENGTH; ++j) {
+-                        value=enumValue(context, data32!=NULL ? data32[block+j] : idx[block+j]);
++                        if (data32!=NULL) {
++                            value=enumValue(context, data32[block+j]);
++                        } else if (idx!=NULL) {
++                            value=enumValue(context, idx[block+j]);
++                        } else {
++                            /* data32 and idx are not supposed to be NULL at the same time */
++                            U_ASSERT(false);
++                            return;
++                        }
+                         if(value!=prevValue) {
+                             if(prev<c && !enumRange(context, prev, c-1, prevValue)) {
+                                 return;