Minor tweaks to query planning weights so that when STAT4 is enabled

and functioning, a full table scan is more likely to be selected if
that seems like the fastest solution.  Only do this when STAT4 info
is available because an error has a large potential downside.

FossilOrigin-Name: 0e7e113d9f2c929c1f8a85e2cfad8e2e60f0e8770212b5e5320fb2a2c42911f8

diff --cc manifest
index 04ee23927bcb493ee4cc84ec80dfdd24f9af2e7e,af44176f84bede3a7e453f6e6d6e8ac59536e50a..9f868d856bb606664085e095bde12674516ea9bf
--- 1/manifest
--- 2/manifest
+++ b/manifest
@@@ -1,5 -1,5 +1,5 @@@
- C Fix\sthe\ssqlite3_hard_heap_limit()\sso\sthat\sit\sworks\swith\ssqlite3_realloc64()\nin\saddition\sto\ssqlite3_malloc64().\s\sImprovements\sto\sOOM\sprocessing\sand\ndebugging\saids\sin\sthe\sfuzzcheck\sutility.
- D 2020-10-20T14:40:53.201
 -C Test\scase\supdates.
 -D 2020-10-22T18:16:17.916
++C Minor\stweaks\sto\squery\splanning\sweights\sso\sthat\swhen\sSTAT4\sis\senabled\nand\sfunctioning,\sa\sfull\stable\sscan\sis\smore\slikely\sto\sbe\sselected\sif\nthat\sseems\slike\sthe\sfastest\ssolution.\s\sOnly\sdo\sthis\swhen\sSTAT4\sinfo\nis\savailable\sbecause\san\serror\shas\sa\slarge\spotential\sdownside.
++D 2020-10-22T18:50:30.660
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  F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@@ -1883,7 -1883,7 +1883,8 @@@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a9
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diff --cc manifest.uuid
index 871e6c40f015df47003e6f7447bcfeb5179de3f6,cb9d3e2ade9fdd9de5e74f5e4ab9bd3ccbcd0e11..42810880bde8fec0f7fa37051b5e738060829ddb
--- 1/manifest.uuid
--- 2/manifest.uuid
+++ b/manifest.uuid
@@@ -1,1 -1,1 +1,1 @@@
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++0e7e113d9f2c929c1f8a85e2cfad8e2e60f0e8770212b5e5320fb2a2c42911f8