Correction to PE wwunpack overread guard

The prior fix for the wwunpack overread in commit
89cd0df was a little too late, but
also removed an earlier, smaller guard for a write.

This commit just moves the larger guard a little earlier to protect
against both.

Resolves: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=60655

libclamav/wwunpack.c

@@ -232,19 +232,23 @@ cl_error_t wwunpack(uint8_t *exe, uint32_t exesz, uint8_t *wwsect, struct cli_ex
 
     if (CL_SUCCESS == error) {
 
-        exe[pe + 6] = (uint8_t)scount;
-        exe[pe + 7] = (uint8_t)(scount >> 8);
-
-        if (!CLI_ISCONTAINED(wwsect, sects[scount].rsz, wwsect + 0x295, 4)) {
+        // Verify minimum size of exe before dereferencing.
+        if (!CLI_ISCONTAINED(exe, exesz, exe + pe + 0x50, 4)) {
             cli_dbgmsg("WWPack: unpack memory address out of bounds.\n");
             return CL_EFORMAT;
         }
-        cli_writeint32(&exe[pe + 0x28], cli_readint32(wwsect + 0x295) + sects[scount].rva + 0x299);
 
-        if (!CLI_ISCONTAINED(exe, exesz, exe + pe + 0x50, 4)) {
+        // Verify minimum size of wwsect before dereferencing.
+        if (!CLI_ISCONTAINED(wwsect, sects[scount].rsz, wwsect + 0x295, 4)) {
             cli_dbgmsg("WWPack: unpack memory address out of bounds.\n");
             return CL_EFORMAT;
         }
+
+        exe[pe + 6] = (uint8_t)scount;
+        exe[pe + 7] = (uint8_t)(scount >> 8);
+
+        cli_writeint32(&exe[pe + 0x28], cli_readint32(wwsect + 0x295) + sects[scount].rva + 0x299);
+
         cli_writeint32(&exe[pe + 0x50], cli_readint32(&exe[pe + 0x50]) - sects[scount].vsz);
 
         // Bounds check not required here, because we know exesz > pe + 0x50 + 4