Merge the btreeNext() assertion bug fix from trunk.

FossilOrigin-Name: 11bd66e09035039fbfc4c5631196962dd3f2e6634f5123a7b2fec17aeaaab07b

manifest

@@ -1,5 +1,5 @@
-C Consider\sdoing\sa\spartial\stable\sscan\sto\sfulfill\san\sIN\soperator\srather\nthan\susing\san\sindex.\s\sTry\sto\spick\sthe\splan\swith\sthe\slowest\scost.
-D 2018-06-08T18:22:10.089
+C Merge\sthe\sbtreeNext()\sassertion\sbug\sfix\sfrom\strunk.
+D 2018-06-08T19:54:07.050
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 F Makefile.in bfc40f350586923e0419d2ea4b559c37ec10ee4b6e210e08c14401f8e340f0da
@@ -436,7 +436,7 @@ F src/auth.c a38f3c63c974787ecf75e3213f8cac6568b9a7af7591fb0372ec0517dd16dca8
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 F src/bitvec.c 17ea48eff8ba979f1f5b04cc484c7bb2be632f33
 F src/btmutex.c 8acc2f464ee76324bf13310df5692a262b801808984c1b79defb2503bbafadb6
-F src/btree.c ae7687faa330562d36cede3375fdc316bff068e9216322d0dfbb3749333e5d3d
+F src/btree.c 06690f5ad144c5e69dfb68d5ec8ee4819c6d40f4b8bc77aa97975938f59d928c
 F src/btree.h ab639c4b9b210b8f4cd7a3a922af73df9a3f27c1d124267339fd73ef8619f488
 F src/btreeInt.h 620ab4c7235f43572cf3ac2ac8723cbdf68073be4d29da24897c7b77dda5fd96
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@@ -1731,10 +1731,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
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-Z f877a3ca3a67b98847cd7a3f31dd6a75
+Z b50b0532bda90928b75cfc1466c6bb97

manifest.uuid

@@ -1 +1 @@
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+11bd66e09035039fbfc4c5631196962dd3f2e6634f5123a7b2fec17aeaaab07b

src/btree.c

@@ -5589,7 +5589,16 @@ static SQLITE_NOINLINE int btreeNext(BtCursor *pCur){
 
   pPage = pCur->pPage;
   idx = ++pCur->ix;
-  assert( pPage->isInit );
+  if( !pPage->isInit ){
+    /* The only known way for this to happen is for there to be a
+    ** recursive SQL function that does a DELETE operation as part of a
+    ** SELECT which deletes content out from under an active cursor
+    ** in a corrupt database file where the table being DELETE-ed from
+    ** has pages in common with the table being queried.  See TH3
+    ** module cov1/btree78.test testcase 220 (2018-06-08) for an
+    ** example. */
+    return SQLITE_CORRUPT_BKPT;
+  }
 
   /* If the database file is corrupt, it is possible for the value of idx 
   ** to be invalid here. This can only occur if a second cursor modifies