Fix an error in debugging output discovered while working on the problem

with RETURNING reported by [forum:/forumpost/d010a26798|forum post d010a26798].

FossilOrigin-Name: 3ae9127f15f8c94493f14b46a09679a8219d66e16a0e984e2cad513d5c41ec86

manifest

@@ -1,5 +1,5 @@
-C Add\smissing\s"const"\son\svariables\sin\srecent\sRBU\sfixes.
-D 2023-01-13T18:20:40.205
+C Fix\san\serror\sin\sdebugging\soutput\sdiscovered\swhile\sworking\son\sthe\sproblem\nwith\sRETURNING\sreported\sby\s[forum:/forumpost/d010a26798|forum\spost\sd010a26798].
+D 2023-01-13T19:00:38.238
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -642,7 +642,7 @@ F src/pcache1.c dee95e3cd2b61e6512dc814c5ab76d5eb36f0bfc9441dbb4260fccc0d12bbddc
 F src/pragma.c 23e74aaa441a03e6d97098db5883f53ee50cc50d294ecefb916437b8484012b3
 F src/pragma.h e690a356c18e98414d2e870ea791c1be1545a714ba623719deb63f7f226d8bb7
 F src/prepare.c 9ebd3a1b12bbd1951f0d6db850f32cf5d4547a6ab8bb9e958d75dfbe4e60d0a3
-F src/printf.c ff4b05e38bf928ff1b80d3dda4f977b10fe39ecbfe69c018224c7e5594fb2455
+F src/printf.c a40bb6b23e40d176685f55837f856e5908dcc9ade490d33359089f5c9528e3be
 F src/random.c 606b00941a1d7dd09c381d3279a058d771f406c5213c9932bbd93d5587be4b9c
 F src/resolve.c efea4e5fbecfd6d0a9071b0be0d952620991673391b6ffaaf4c277b0bb674633
 F src/rowset.c ba9515a922af32abe1f7d39406b9d35730ed65efab9443dc5702693b60854c92
@@ -2069,8 +2069,11 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P bd8fa10e59f58886e10c84ea9934fa1b5f491aac2eff302757a76d2d36d59b69
-R b0128c6ff9efe26a006547103763567b
+P 9b8dcd79050f9bfa745271f51377b38cfed4d8ce41a36b773a30799d69f7b943
+R 0521ee306058f596b350b31285652eb0
+T *branch * returning-is-null-fix
+T *sym-returning-is-null-fix *
+T -sym-trunk *
 U drh
-Z 73010cbd896bf55e27536733698725c5
+Z d49ed173206544b7d12409fb165b17a9
 # Remove this line to create a well-formed Fossil manifest.

manifest.uuid

@@ -1 +1 @@
-9b8dcd79050f9bfa745271f51377b38cfed4d8ce41a36b773a30799d69f7b943
+3ae9127f15f8c94493f14b46a09679a8219d66e16a0e984e2cad513d5c41ec86

src/printf.c

@@ -884,6 +884,7 @@ void sqlite3_str_vappendf(
       }
       case etSRCITEM: {
         SrcItem *pItem;
+        Select *pSel;
         if( (pAccum->printfFlags & SQLITE_PRINTF_INTERNAL)==0 ) return;
         pItem = va_arg(ap, SrcItem*);
         assert( bArgList==0 );
@@ -897,9 +898,7 @@ void sqlite3_str_vappendf(
           sqlite3_str_appendall(pAccum, pItem->zName);
         }else if( pItem->zAlias ){
           sqlite3_str_appendall(pAccum, pItem->zAlias);
-        }else{
-          Select *pSel = pItem->pSelect;
-          assert( pSel!=0 );
+        }else if( (pSel = pItem->pSelect)!=0 ){
           if( pSel->selFlags & SF_NestedFrom ){
             sqlite3_str_appendf(pAccum, "(join-%u)", pSel->selId);
           }else{