fix(results): restore guarded multi-result advance

Author: quinnj

src/MySQL.jl

@@ -55,12 +55,13 @@ function clear!(conn, result::API.MYSQL_RES)
     if conn.mysql.ptr != C_NULL && result.ptr != C_NULL
         while true
             if API.fetchrow(conn.mysql, result) == C_NULL
-                nxt = API.nextresult(conn.mysql)
-                if nxt === nothing
+                if API.moreresults(conn.mysql)
+                    finalize(result)
+                    @assert API.nextresult(conn.mysql) !== nothing
+                    result = API.useresult(conn.mysql)
+                else
                     break
                 end
-                finalize(result)
-                result = API.useresult(conn.mysql)
             end
         end
         finalize(result)

src/execute.jl

@@ -204,18 +204,19 @@ function Base.iterate(cursor::TextCursors{buffered}, first=true) where {buffered
     cursor.cursor.result.ptr == C_NULL && return nothing
     if !first
         finalize(cursor.cursor.result)
-        nxt = API.nextresult(cursor.cursor.conn.mysql)
-        if nxt === nothing
+        if API.moreresults(cursor.cursor.conn.mysql)
+            @assert API.nextresult(cursor.cursor.conn.mysql) !== nothing
+            cursor.cursor.result = buffered ? API.storeresult(cursor.cursor.conn.mysql) : API.useresult(cursor.cursor.conn.mysql)
+            if buffered
+                cursor.cursor.nrows = API.numrows(cursor.cursor.result)
+            end
+            cursor.cursor.nfields = API.numfields(cursor.cursor.result)
+            fields = API.fetchfields(cursor.cursor.result, cursor.cursor.nfields)
+            cursor.cursor.names = [ccall(:jl_symbol_n, Ref{Symbol}, (Cstring, Csize_t), x.name, x.name_length) for x in fields]
+            cursor.cursor.types = [juliatype(x.field_type, API.notnullable(x), API.isunsigned(x), API.isbinary(x), cursor.cursor.mysql_date_and_time) for x in fields]
+        else
             return nothing
         end
-        cursor.cursor.result = buffered ? API.storeresult(cursor.cursor.conn.mysql) : API.useresult(cursor.cursor.conn.mysql)
-        if buffered
-            cursor.cursor.nrows = API.numrows(cursor.cursor.result)
-        end
-        cursor.cursor.nfields = API.numfields(cursor.cursor.result)
-        fields = API.fetchfields(cursor.cursor.result, cursor.cursor.nfields)
-        cursor.cursor.names = [ccall(:jl_symbol_n, Ref{Symbol}, (Cstring, Csize_t), x.name, x.name_length) for x in fields]
-        cursor.cursor.types = [juliatype(x.field_type, API.notnullable(x), API.isunsigned(x), API.isbinary(x), cursor.cursor.mysql_date_and_time) for x in fields]
     end
     return cursor.cursor, false
 end